6th Gen The new and improved Hoenn Dex! Now with 20% more awesomeness :33

[Polygon-Z]

We already know that the Hoenn dex will be expanded in some form, as Phoebe of the Elite 4 uses a Dusknoir according to the recent Corocoro scans.
In my opinion, I think the new Pokedex will only be expanded to include new Pokemon that are evolutions or pre evolutions of pokemon in the Hoenn dex. I think this list could safely include Magnezone, Probopass (The power plant would be the perfect place for them to evolve), Froslass, Gallade, and a few others. I don't think all of the Sinnoh evolutions will be included, but at least a few of them will.
An interesting thing to note is the Safari zone. Previously, it contained only pokemon foreign to Hoenn, specifically, Kanto and Johto pokemon. In emerald, there was an expansion that included some Johto pokemon not in the regional dex, including Mareep and Shuckle. It could be that the new dex is expanded to include not only the Sinnoh evolutions, but it could also include these Johto pokemon.
Expanding upon this further is the idea of the whole Safari zone being expanded, and including Sinnoh, Unova and Kalos pokemon. This seems pretty unlikely, since this would likely take the original Hoenn dex and warp it beyond recognition (this is a remake, after all.), plus the other two safari zones in FR/LG and HG/SS didn't include any new Pokemon pre-credits.
I would think that only a few Sinnoh evolutions will make the cut, but that's just my opinion. It could be anything, really.

 

[OmegaRuby and AlphaSapphire]

We already know that the Hoenn dex will be expanded in some form, as Phoebe of the Elite 4 uses a Dusknoir according to the recent Corocoro scans.
In my opinion, I think the new Pokedex will only be expanded to include new Pokemon that are evolutions or pre evolutions of pokemon in the Hoenn dex. I think this list could safely include Magnezone, Probopass (The power plant would be the perfect place for them to evolve), Froslass, Gallade, and a few others. I don't think all of the Sinnoh evolutions will be included, but at least a few of them will.
An interesting thing to note is the Safari zone. Previously, it contained only pokemon foreign to Hoenn, specifically, Kanto and Johto pokemon. In emerald, there was an expansion that included some Johto pokemon not in the regional dex, including Mareep and Shuckle. It could be that the new dex is expanded to include not only the Sinnoh evolutions, but it could also include these Johto pokemon.
Expanding upon this further is the idea of the whole Safari zone being expanded, and including Sinnoh, Unova and Kalos pokemon. This seems pretty unlikely, since this would likely take the original Hoenn dex and warp it beyond recognition (this is a remake, after all.), plus the other two safari zones in FR/LG and HG/SS didn't include any new Pokemon pre-credits.
I would think that only a few Sinnoh evolutions will make the cut, but that's just my opinion. It could be anything, really.

The safari zone expansion in Emerald was post game, so any expansion for ORAS' SZ can be post game as well, thus not changing the dex too radically.
I think all of them could make it, with Magnezone and Probopass evolving around New Mauville. They can have all the stone and trade evolutuion items. If the item evolutions and the Johto SZ Pokemon from the post game Emerald SZ expansion are included it'll include Gliscor too.

 

[Aeroblast]

Actually, if it was like HGSS's Pokedex, then the Hoenn Pokedex wouldn't get changed at all. HGSS's updated Pokedex only included evolutions that didn't involve items - the reason being, of course, that they could place the items in Kanto (post-game) and thus you wouldn't normally be able to evolve them.

The ones it kept are all level-up w/ a certain move. Because there'd be no way to prevent you from accessing it through normal gameplay until you got to Kanto - they just learn the moves naturally. So they were added to the Johto Dex. This is why we have Mamoswine and Ambipom, but not Gliscor or Porygon-Z.

Hoenn, however, has no Pokemon like that. Every single Pokemon in Hoenn that has a cross-generational evolution or pre-evolution is based on items. So, nothing would be added.

I see your point.

It's a fine margin, though, and the rule could be more lenient to open up for evolutions using other methods.

 

[Salzorrah]

Seeing as Phoebe's Dusknoir appears in game, I see no doubt that we see the likes of Roserade, Gallade, Froslass, and others, in game too since they are cross-generational.

 

[Yato]

It would be odd for GF to only include Dusknoir and not any of the other Gen. IV evos., so I can definitely see them appear! Dunno about Budew; like I stated earlier it could be made available early on in Petalburg Woods or something, but at the same time, Roselia can be found near Mauville, which isn't to far in-game. Plus, babies aren't exactly the easiest Pokemon to raise since a majority aren't that strong, even in earlier parts of the games.

Still hoping that GF adds even a few more Pokemon with types that don't appear much in Hoenn, namely Ice and Ghost. If there were one more Ghost type, Phoebe would be able to have a diverse team. (Given, she could use Shedinja in place of one of her Banettes, but newer players might not be able to counter it, so it probably wouldn't be included.) Likewise, if there were one-two more Ice types, Glacia could have a diverse team. (I'm assuming Froslass will be added and will replace one of her Glalie.)

 

[Xebelleon]

I can really see Glacia and Wallace as getting some quality movepool change.
Azumarill is now Water/Fairy

 

[Pepperton]

I really don't see a valid reason as to why they wouldn't add Budew as well as Roserade. That wouldn't make sense, and look incomplete in the dex. Also would give them an opportunity to put it earlier in the game, like the routes near Petalburg or in the Woods. Phoebe having a Dusknoir is a pretty solid indication that they're going to be adding evolutions from later generations into the dex. Other than that, there won't be much altered.

 

[OmegaRuby and AlphaSapphire]

I agree with Pepperton, it wouldn't make sense to leave out the pre evolutions. Hoenn introduced the first incenses so they'll likely add the rest to make it possible to breed if they don't add them early (I would like to see them in the wild though).

 

[Altairis]

Well the only reason they weren't int the games before was because they didn't exist, so of course there's no reason to edit them out now. In the past couple of games they seem to be adding more popular Pokemon instead of keeping them away under lock and key, so I think we'll see stuff like Eevee and Dragon-types before the game ends.

 

[OmegaRuby and AlphaSapphire]

Well the only reason they weren't int the games before was because they didn't exist, so of course there's no reason to edit them out now. In the past couple of games they seem to be adding more popular Pokemon instead of keeping them away under lock and key, so I think we'll see stuff like Eevee and Dragon-types before the game ends.

Strangely they have kept some popular ones under lock before, such as Pikachu's line not even being added to B2W2's dex. Gen V was strange for keeping the mascot out... Eevee being out of Gen III is sort of like that. Interestingly they're the starters for Yellow (Pikachu being the players and Eevee Blue/Green's).

 

[Yato]

Hoenn already has quite a few Dragon types as is (Kingdra, Flygon, Bagon line, Altaria, the Latis, Rayquaza), so I'd rather not see anymore added x_x Eevee's a possibility; part of me wants to say "YES PUT IT IN THERE PLEASE" because I love it and its Eeveelutions (plus, Glacia could have a Glacia (Glaceon) :D), but at the same time, I sort of hope it isn't. Though, even if it isn't available, one could just easily transfer it over from Pokebank/via trading unless the games prevent them from doing such. (I doubt that'd be the case, though.)

 

[Pinkie-Dawn]

Hoenn already has quite a few Dragon types as is (Kingdra, Flygon, Bagon line, Altaria, the Latis, Rayquaza), so I'd rather not see anymore added x_x Eevee's a possibility; part of me wants to say "YES PUT IT IN THERE PLEASE" because I love it and its Eeveelutions (plus, Glacia could have a Glacia (Glaceon) :D), but at the same time, I sort of hope it isn't. Though, even if it isn't available, one could just easily transfer it over from Pokebank/via trading unless the games prevent them from doing such. (I doubt that'd be the case, though.)

Actually, Hoenn could use a few more Dragon type into the mix if we want to replace Drake's two Bagons to make sure no gym leader nor Elite Four uses 1-2 Pokémon from the same family line.

 

[Yato]

Actually, Hoenn could use a few more Dragon type into the mix if we want to replace Drake's two Bagons to make sure no gym leader nor Elite Four uses 1-2 Pokémon from the same family line.

He had Shelgon, Kingdra, Altaria, Flygon, and Salamence in Emerald; don't see why he can't use that same team in ORAS :3

EDIT: While it's true Shelgon/Salamence is from the same line, I think him having five fully evolved Dragons might be too much @_@ (Plus, none of the other E4/Champion Dragon specialists had more than four fully evolved Dragons on their team.)

 

[OmegaRuby and AlphaSapphire]

Actually, Hoenn could use a few more Dragon type into the mix if we want to replace Drake's two Bagons to make sure no gym leader nor Elite Four uses 1-2 Pokémon from the same family line.

You mean to say 2-3 right? As the 1 in 1-2 implies they should have 3 or more from the same family line 0_o
What about alternate evolutions such as Froslass and Glalie?
Glacia was the biggest victim having 3 from the Spheal family. But now that she may get Froslass it won't be as bad.
Actually Phoebe may be in worse condition now unless they add more ghost types...hopefully not Shedinja...

 

[Pinkie-Dawn]

He had Shelgon, Kingdra, Altaria, Flygon, and Salamence in Emerald; don't see why he can't use that same team in ORAS :3

EDIT: While it's true Shelgon/Salamence is from the same line, I think him having five fully evolved Dragons might be too much @_@ (Plus, none of the other E4/Champion Dragon specialists had more than four fully evolved Dragons on their team.)

How is having five fully evolved Dragons too much? As long as you have an Ice type or Fairy type in your team, the only main issue with a Dragon specialist's team is using 2-3 Dragon types from the same line, which is lazy.

What about alternate evolutions such as Froslass and Glalie?

Split evolutions are in a strange limbo. They're both from the family, yet they have different stat spreads/typings to make them unique.

 

[OmegaRuby and AlphaSapphire]

Unfornutely even if they add more mons of their type I don't think GF will change their teams much.
It's also possible it'll only be the Sinnoh evolutions.
As long as they give Phoebe another ghost (that isn't Shedinja which is already in the Hoenn dex anyways) I'll be fine if they don't add anymore.

 

[Altairis]

Hoenn already has quite a few Dragon types as is (Kingdra, Flygon, Bagon line, Altaria, the Latis, Rayquaza), so I'd rather not see anymore added x_x Eevee's a possibility; part of me wants to say "YES PUT IT IN THERE PLEASE" because I love it and its Eeveelutions (plus, Glacia could have a Glacia (Glaceon) :D), but at the same time, I sort of hope it isn't. Though, even if it isn't available, one could just easily transfer it over from Pokebank/via trading unless the games prevent them from doing such. (I doubt that'd be the case, though.)

Honestly, I wasn't sure which ones had already been included and I was just thinking of "cool popular Pokemon" and Dragon-type came to mind since they were my personal favorite xD

 

[ThePokeRaf]

I think that the PokeDex is perfect. It's a gameboy advance and it has a new slick design alongside a new in game design which makes it distinctive compared to the others.

 

[Salzorrah]

We need basically more rare types in the game like Ghost, Ice, and Fairy. Maybe the Ghastly line, Eevee line, Flabebe line, and the Snover line could appear in Hoenn in the main game?

 

[OmegaRuby and AlphaSapphire]

Flabebe with tropical flowers?
Maybe they'll add in Shellos as it was meant to be a Hoenn Pokémon.