Being "set in all regions" doesn't necessarily mean that they will all be featured equally. It just means that the writers can take Ash to any region that they want. The first region will probably be Galar, and I'm sure that it will get the love it deserves, but after that Ash can leave and spend time in another region.
I've come to the conclusion that reverting the title of the series simply to "Pocket Monsters" is a way to finally separate the anime from the games. Starting now, the anime will serve to promote the entire franchise, with the core games being only one part of that. I believe that the anime will become completely reactive to whatever happens to be hot with the Pokemon franchise at the time. In November, the new hotness will be Sword and Shield, and as such the anime will give it plenty of attention. But when the next big thing comes along (Sinnoh remakes/Masters expansion/etc.) the show will switch on a dime to promote that.
I believe that this will be the last Pokemon series, but that it will continue indefinitely. Instead of creating a new series for every core game, each new release will be treated with their own arc in this new long-form series. The best example I can think of would be Battle Frontier. It largely existed as a promotion for FRLG, even though it was still part of Advanced Generation. Obviously this was done due to Gen 4 being delayed, but I think this helps point the way for the future of the series. Ash will continue from one major arc to another, without the need for a soft reboot.
By the way if there IS a Sinnoh arc next year, I hope it will be Battle Frontier part 2.
