Honestly an Ash Ketchum themed Pokémon spinoff in the style of something like Dragon Ball Z Kakarot would be pretty cool.
A LarryBoy game (Yes, I know they already made 2 but both of them were essentially GBA and PS2 Shovelware) inspired by Batman Arkham Knight and Spider-Man 2 (PlayStation 2) (At least gameplay wise) would be pretty fun.
I would like to see a first & third person Pokémon action adventure RPG based of the main series games, but for PC and with modern detailed graphics, maybe made with the Unreal engine. With a conversation system with full voice acting that isn't one sided so the player also has dialogue. Also full voice acting for all the Pokémon cries in the game like in the anime.