I'm just going to completely disregard the Turn-Base hating. For the record, I really down they are killing turn-base or turning it into an ATB.
Funny, remember someone saying the show make the game like Xenoblade. While I thought it wasn't a bad idea, I thought it would be more for a spinoff.
Seems like that person may get his wish, if this is true, thanks to Mario and Zelda.
I wouldn't mind at all if they remade R/B/Y, but combined it into one game. They could redo each generation as a new entry. Pokemon Kanto for 2019, Pokemon Johto for 202X, etc.
If they are going to do this, this does seem like a good place to reboot the whole series. So many ideas they can do for the first regions, if they start all over. Wouldn't be tied down, like with just a remake. Could be whole different storyline. Places could be completely different while still fitting the regions.
I'm seriously hoping it's something that spans multiple regions.
If it does span 2+ regions, there's only one thing I can really think of that'd work with the game. The current Pokemon format would have to be altered (but not flat-out changed so you couldn't transfer in old Pokemon from old games), maybe so Pokemon can level beyond level 100, since 100 will be pretty easy to achieve in a game that has multiple regions that are actually fleshed out and not just some sort of post-game thing. On top of that it might be a good idea to have the levels of trainer's Pokemon in regions other than the default possibly scale with your Pokemon's levels in some way. That's the only thing I can think of that works.
Would be cool, if they did more than one or two regions per game. They could very well make it harder to level up or make the level bigger without abandoning the old Pokemon. They could update the old Pokemon to the new leveling system. If they do allow old Pokemon on the new system, they probably wouldn't let you do that vi versa.
Also, rather they have a new leveling system or not, they can just make you Switch Pokemon every region until the last one and post game.
The only way they can make a major change is if they try to make the game open world, but that also creates several issues. You'd br able to just wander to areas where trainers and Pokémon are way too strong meaning it would be a lot harder to catch Pokémon and battle. This would also make levelling up your Pokémon very difficult. That also makes Pokémon inhabiting certain areas a little more difficult because they'd probably get rid of the closed off routes making a lot of places just big fields, possibly creating the same issue Sun and Moon had where certain Pokémon are either in very specific patches of grass or having a very, very low chance of encounter. They could get rid of tall grass but then Pokémon would appear on screen and there would either be too few or too many causing something like slowdown or cluttering areas.
They could still close off areas. Besides, if they want to go to places that are obviously too strong for them, that's the players fault. Of course, there should be guides to go the easiest direction.
That's the biggest issue. Will they actually show Pokemon wondering around or still just keep them mostly "hidden" until battle. They could also do a balance of both. This would avoid some of the problems of too many Pokemon on screen and too little Pokemon to catch.