I don't think that would be a pokemon game, more of a kind of wifi battle simulator. Pokemon is an RPG. In RPGs, you always go from being weak to being strong. If you go from strong and staying strong throughout the game, it would be very boring and wouldn't seem like a game.
If there was an adult-targeted pokemon game it would definitely need to be focused on the story, because games that are targeted towards adults tend to try and have better stories than ones targeted towards kids, not to say that games targeted towards kids are bad, however, like, in my opinion, how Pokemon Black and White were great games that'srightfightme.
I would love to play a game like Pokemon Colosseum. It is my favourite Pokemon game ever, so to not only have a nostalgia trip, but to also play a game that is actually good, is something I really want to do.