It won't be Snap or a Stadium-esque game
Quotes from Masuda
>"Photography wasn't as widely spread in those days," he says. "Now everyone has a camera and can take photos whenever they want. Releasing it in that same form wouldn't be as interesting these days. Maybe there's a new idea, though."
>Masuda said, "It kind of goes back to the core philosophy of Pokémon as a brand: We really want to excite people and surprise them with new things they weren't expecting. The original games, of course, were 2D and in black and white, and seeing them in 3D was a stark contrast... it was kind of a huge surprise for players. Nowadays, the Pokémon are already in 3D, and I'm not sure that better graphics would be quite as impactful or impressive. So in order to come back to the Stadium series, I think we'd need to have some sort of new invention to justify it."
Tl;dr Snap is dead because everyone has a camera on their phone nowadays, and Stadium is dead is because the main games are already 3D