I have a question if by chance according to recent leaks the next game isn't Gen 8 but a sort of remake/reboot of Red and Blue what will the anime do? Will they expand the Alola region with anime original content or go to Kanto probably for the Alola gang to challenge the Gyms with Ash and Ash get another shot at the Kanto league?
Also what would they do if its the after 100 years sequel? This would be impossible to explain in the anime.
I'm pretty sure those leaks are fake, but if true, it would be handled the same way previous remakes are: Gen I remakes were still Gen III: the Gen III anime continued. Gen II remakes were still Gen IV: Gen IV anime continued. Gen III remakes were still Gen VI: the Gen VI anime continued.
If it truly is another set of Gen I remakes, it would be a continuation of Gen VII, not Gen VIII. (
unless a whole new set of brand new Pokémon is unveiled) And as long as it's Gen VII, then the Gen VII anime will continue regardless of where the current Gen VII game is taking place, Alola, Kanto, Sinnoh, or somewhere else.
To break down your possibilities:
Will they expand the Alola region with anime original content
This is possible. HGSS caused Sinnoh to have some anime-original content like the Johto Festa.
When ORAS came out, Ash and Serena got the ORAS Pokédexes, and there was an anime-original storyline for Team Flare.
It's definitely possible that they could just integrate the next games' storylines and expand Alola with anime-original content like these last two examples I just gave above.
go to Kanto probably for the Alola gang to challenge the Gyms with Ash and Ash get another shot at the Kanto league?
This is possible as well -- the last Kanto remakes in Gen III caused Ash to revisit Kanto. However, he did not redo the gyms. I can see him revisiting Kanto again just as he did in Gen III; however, I don't see him redoing the gyms. I see him doing something else how he did in Gen III.
btw, most of this entire post I've made is only under the scenario that the leak is true. I personally believe the leak to be false.