As Weedle pointed out, I pointed out concept arts being posted a while ago on one of the official twitters.
Sun and Moon will probably last another year. It is possible that we will go back to Kanto or Johto once more. With it being remakes, Kanto is likely, but I don't know what it could be.
From what I have seen in the anime, it looks like they are building up toward the Rainbow Rocket or at least Team Rocket arc. This would include Looker and possibly Anabel. Since Anabel was in Kanto last we saw her, I wouldn't be surprised if they combine the Rocket, Necrozma and UB arcs together.
Since we have already been to Poni Island in the anime, it is possible that there won't be much going on there. But still, where does that leave us.
It is hard to say right now to be honest, but right now, everything is looking to return to Kanto and possibly the return of more old characters. Dawn has not yet been to Kanto, and she is supposed to be currently in Johto. Dawn could make a return. Virgil would also make some sense.
All and all this is how I think everything will be.
Poni Island Arc (No more than 5 episodes)
Pokemon League Arc ill the end of the year)
Then next year, we could return to Kanto.
Maybe a Festival Arc or maybe even Ash's party at becoming the Champion of Alola (Don't get your hopes up, just an idea and probably not possible.)
Team Rocket Arc
With how powerful Ultra Necrozma is, we could see a return of Zygare and Greninja. Plus in the game, it was a Dark Type you needed to stop Necrozma in most cases.
Before we can guess what will clearly happen, we need more info about the games. We have never had a second remake before.