To start i'd like to say i'm curious to know how you'll design this game such as the things you listed in the features for example retyping and re-doing stats on some pokemon, i'm also looking forward to the difficulty of the game the one thing i dislike about the official games is how incredibly easy they are when playing through the story on the other hand i really enjoy games such as Pokemon Reborn, Insurgence and Rejuvenation which all have a difficulty curve along with a great story. There's just not much fun if you can just sweep the whole game with your starter and a HM slave.
I also like that you're planning on doing Gym Leader rematches as they're always fun to do, i'd be good to see them get increasingly more competitive as the rematches progress which makes me wonder what is their base difficulty going to be like will they have a full team of 6? Will they have good movepools or anything like that, or would that only be for rematches? I'm also curious to know if you're doing them as somewhat traditional Monotypes, Theme based or even just a mix of various types for a more well rounded battle for example like Cynthia and Gary who never had a single type they used whatever they thought worked well together, Personally i like the whole Monotype idea in terms of competitive play such as Showdown the only Tier i play would be Monotype i just find it enjoyable. I'd also like to know if you've already got plans for gym leaders / elite four or if you could maybe add people from the community. There was another fan game somewhere which had a contest in which participants were added into the game as Gym Leaders which i thought was a really good idea. Personally i think i'd be awesome to be apart of somebody else's game though it's entirely up to you what you do.
Another thing i wanted to go over is the Hidden ability's, It's nice that each encounter will have a fair chance of having a hidden ability however does that mean that one of the ability's if in the case there were 2 normal ability's + the hidden does one get removed? for example say Ability 1 is Trace Ability 2 is Synchronise and the hidden ability is Telepathy does that mean either of the normal ability's will be removed for the hidden ability to take up that slot or will it be 3 normal abilities if this makes any sense?
Because personally i'd prefer if there was some sort of Item or NPC which changed the ability such as a Dream Capsule (name example not actually referring to an actual item) or an NPC which does some sort of magic for the cost of money / heart scale or something. I'm not just curious to know how you intend on going by it but i feel like Hidden abilities shouldn't be so easy to come by you know what i mean? they're usually an effective ability which can help out a lot in a battle so i feel like you should at least work for them in some regard but that's just my personal opinion.
Another thing is the shiny rate, sure everybody loves shiny's but if the chances are to high then they'll lose their value on the other hand if they're to low the player may feel frustrated about trying to find one. It's up to you how often you feel would be good but i think a 1/500 or less would be good, i think the highest possible chance of getting one without say Dex Nav chaining is 1/512 in Friend safari's or Masuda method shiny charm so no higher than that would be nice. Again just my personal opinion.
Lastly i'd like to ask what your upcoming idea's for the game may include it may be a little early to ask since you haven't got your first demo out yet but have you considered Custom Mega's? I'm sure you can relate that since XY came out and introduced mega evolution that there's always been at least one pokemon you wish had a mega and since you're making your own game you have the power to make it. Pokemon Insurgence has some amazing designs you could use for inspiration if you thought about adding custom mega's, However it'd take some time to come up with a design, sprite it, give it a balanced stat layout and ability so i can imagine you either not wanting "fakemon" in your game or if it'll be to much work for you / your team. But just a thought.
Back to the original question though are there any features you feel like adding at some point into the game? i'm curious to know what you feel like doing with your game. so far it seems promising i'm interested to see how it turns on when you get your first release out there.
I'd also like to apologize as this message is somewhat long as well as somewhat unclear i'd assume but i hope you can understand what i mean. Anyway good luck with your development (:
