If Switch game is indeed Kanto then i dont think it will be 20 years later Kanto

First of all we already met grown up Red and Blue and we just battled them. It wouldnt be very exciting to meet them again right away
Second thing: who would be the enemy? Team Rocket gave up on Kanto at the end of RBY. In GSC they're focused on Johto. Now they're Rainbow Rocket who's aim is conquering different universes. Giovanni already has Mewtwo. Why would he go back to Kanto when he can freely travel through dimensions?
Finally Lillie and Lusamine's story was changed in USUM. They dont need to travel to Kanto anymore while Gladion trained there for a little while and came back to Alola

I really dont think we're getting Kanto 20 years later sequels.

Its probably going to be FRLG remakes but with some bells and whistles from other gens (megas, z-moves, maybe other characters like Sycamore coming to get Kanto starters or younger Kukui) hence why people like riddler call it reboot. But sequel, imo, makes no sense with what we know from gen 7 games