Yeah, i'm in the same boat, I've been fiending this game. I can't believe they haven't put anything like this out. My only thinking is they figure it has to be massive, and once things go 3D. Well, moving "block by block" like you can in pokemon red blue (etc.) is just well hard especially in 3d. Think about how many levels you really go through with pokemon, and how expansive of a game it really is. Now, at the same time, I feel once they got the initial game down sequels would be a breeze, and I would hope they look to make it into more of a long term profit.
Honestly, going back and playing red/blue. A lot of the additions they made in subsequent games I feel aren't necessary. Yes it's additions to do, but the originals are still so much fun to play.
Another thing I would like to add Pokemon stadium I always felt the attacks were always a little much. And battles weren't as quick as they are in the game cube games because of it. (This makes grinding hard which is a necessary part of the game at some points.)
Now, something else I don't understand is, pokemon snap had levels that were pretty well designed the pokemon fit there in there natural habitat. I just wonder how this art would transfer. I think that it could come off clunky looking in this style of game.
I wouldn't be surprised if they've tried making this game like 3-5x, they just lack visionary direction for it. And even thinking about small things like...do you see the pokemon when you walk through the long grass? or do they just pop up. Do you actually have to throw your pokeball? What happens to a pokemon after you caused it to faint? Can't you just catch it? etc.