Hmm. Well I brought this up on another thread the other day but has anyone ever considered doing a Fire Red/Leaf Green hack built using the Emerald game engine? Here's why I bring this up;
1: Prior to the Emerald version EV training required you to breed and re-breed almost constantly to get the right nature and IVs in addition to egg moves. The everstone being able to influence natures of bred pokemon has made that step a lot easier. Similarly having Flame Body and Magma Armor cut the steps needed to hatch eggs in half was a major plus.
2: On the subject of EVs, much like with getting the right nature/IVs for a pokemon EV training in games older than emerald required you to practically re-do your entire team. With how FR/LG forced you to wait until post-game due to the national pokedex to get eggs this was a huge problem for me when I wanted to go to a special event back in the day to battle other players, and it's still a massive pain in ROM hacks because I would love to use my starting team throughout the game and EV train them to be the best they can be, but I can't do that playing ROM hacks using FR/LG/R/S as the ROM base because the EV reducing berries only got their status as EV reducing berries starting in Emerald. Plus considering that the starters are only female 12 percent of the time it's more of a hassle than it's worth to breed a fresh pokemon with zero EVs to train up all over again.
3: Hoenn's map looks pretty similar to Kanto's. With a bit of work one can take portions of th FR/LG map and overlay it onto Hoenn's. The Resolute pokemon hack did a good job redesigning Hoenn so it's possible to remake Hoenn into Kanto. This adds the bonus of additional towns/cities to the new Kanto Map. One can even add some anime touches here and there without making the game explicitly an anime-themed hack. For example in the first season of the anime there was this trainer, AJ who had this tough sandshrew. He appeared to have been using a Macho Brace to help train his pokemon so one can get the brace off him in an in-game event where he replaces the Winstrate family. I can see plenty of similar examples, especially if Grandpa Canyon from the Prehistoric Pokemon episode is used.
4: There needs to be a proper league tournament. Challenging the elite four may be good and all but it alone is an empty experiance. More hacks need a tournament and if one becomes champion there, they can challenge the elite four in the post game sequence afterward.
5: Another anime tidbit I thought of relates to the contests and battle frontier. By using Emerald as a base there's the matter of the pokemon contests and the battle frontier. Having each frontier facility appear around Kanto like they did in the battle frontier saga would be good to try, though they would be off-limits until post game of course. Besides the Trainer Hill Tower thing seen in Fire Red and Leaf Green is seriously lacking and it makes FR/LG not really worth putting a serious playthrough for. he contests shouldn't be limited to just one town either, more contest halls for the appropriate normal/super/hyper/master ranks is a must, it was pretty annoying seeing just one hall in emerald because of the battle tents.
6: Finally the special/physical split is a must in my opinion for such a game, there's precious few if any pokemon that were used competitively in the 3rd gen because of crap like Mightyena's high attack but Crunch was a special attack to name one example. Mightyena may not be superb, but it can be very strong with the right moves and not having access to it's signature attack due to it being a special attack was a huge mistake. Having a few 4th and 5th gen moves would be vital as well since Scizor without X-Scissor and Iron Head is wrong.
Now a game like I mentioned doesn't have to be exactly like this, I'll still play FR/LG hacks without a problem, but at least enable the emerald breeding mechanics and emerald berry system somehow in future fire red hacks, and enable a proper post game challenge like the battle frontier or something.