Pokémon

mainline

Considering it'd have to be Gamefreak making it most likely, the main problem is graphics, so yes please, ditch the 3D that barely performs at 4 fps (when Monster Hunter Stories 2 gives solid 30 and better-defined monsters with cinematic attacks) and give us back some glorious spritework, like Arceus intended when he gave us Emerald. Or at least make a fancy compromise: how about a 3Desque overworld that is Octopath-style (HD2D), and for the battle rendering keep the presumptions of 3D but use the carton placeholders instead of 3D models like the G6 prototypes did. Betcha we can get some decent 42 fps everywhere this way.

Now, if another, more decent company, takes over development of the mainline games? Yeah by all means try something more like PLA or beyond for the graphics. It was a pretty decent venture.

Gameplay and mechanics-wise, I'm not too married to "old style" (whatever that means. Without Abilities, like in G1? No double or triple battles, like in G2?). That said, more recent gens have had an annoying tendency to go for gimmick-of-the-week and add only like, 2 or 3 new usable Pokémon per gen plus 20 legendaries, so maybe a return to form is required in style as well. I think G4-G5 strikes the sweet spot for that one.