I can understand your perspective, but I think they might be taking a different approach for a Pokémon than what many might be imaging it to be. Obviously, the early anime stuck closely to what was established within the games, but in the years since, when Pokémon has been adapted into other mediums, it has taken a lot of creative liberties, with the one primary constant between all adaptions of the franchise being the Pokémon themselves.
More recent projects like Detective Pikachu, Pokémon Concierge, and the upcoming Aardman series stray away from established character, locations, and the concept of battling, and set out to do their own thing creatively. The same could be said about the cafes, the upcoming park in Tokyo, and the various other pop-event and installations they've had. Only the games and animated series have maintained a heavy focus on Pokémon battles and the traditional regions, where other depictions have been more calming and accessible, attributing to Pokémon's growth as a lifestyle brand.
Because of this, I wouldn't necessarily expect to see Kanto/Johto iconography or Pokémon stadiums. Whatever they go with, I imagine the priority will be creating experiences that allow guests to interact with Pokémon, probably through a combination of costumes, animatronics, augmented reality, and other means. I've thought for a while that they could frame it as being a "Pokémon preserve", which could match the aesthetic of IOA, but perhaps that would be too close thematically to Jurassic Park. If they did go down that route, it would be the best way to implement an attraction that takes some inspiration from Pokémon Snap (which they should do).