I believe that the next generation should reinvent a lot of conventions about the series. I know the term "open world" is something that makes everyone roll their eyes nowadays but I feel that a game in that direction would revitalize the series, Just make a region that's expansive, pretty and interesting. Make exploration an actual thing that's rewarding. It doesn't have to be like BoTW either, the existence of routes to walk through is vital for the series however a region designed with more branched paths to walk though would be better than the railroading we have. Another thing on this issue: No more roadblocking. If you want to go to the lvl 50 route first, you can do that. You'll get your ass kicked, but that's how you tell you're going the wrong way. Much more organic than some dude simply telling you that you can't walk over there. I know roadblocks have been the convention since gen 1, but it's one of the primordial molds that have to be broken. Maybe do something like mario odyssey where there's a gamemode telling you exactly where to go, for the little kidies.

Also, take it down a peg with the new designs, go back to a simpler style with them. I know it's almost impossible since the art direction has become increasingly cartoony and complex but there's a point where you need to turn around a little bit before pokemon from the first generation are incomparable to new ones.

Last but definitely not least, have some difficulty for crying out loud. About 85% of alolan trainers only have one pokemon with them, and a lot of them don't even have a full moveset. I know the game is for children, but at least don't be lazy and implement a difficulty setting. Over-casualization will kill a huge chunk of the fanbase which has stuck from the early days of the series.

That's about it really. If it keeps going the way it's at right now, the pokemon series will be forgotten in two generations.