Satomine Night
The Power of Z!
Official site is up.
No further details, but the trailer is there, at least.
Given how beat up Ash and Pikachu look in that image with Ho-oh flying overhead, my feeling that this movie is a retelling or reimagining of OS (or at least part of OS) is getting stronger. At the very least, I expect a retelling or reimagining of the first episode of the anime.
If nothing else, a retelling or reimagining of OS is a chance for younger and/or newer viewers who never saw OS to see for themselves how Ash and Pikachu's journey began.
Would you want to see other pokemon movies based off Ash's other adventures ?(Jotho, Hoenn,Sinnoh,Unova, and Kalos)
or
Would you still want to see one movie focused on the Alola region?
Personally, it's not a matter of what I want, but a matter of what I expect. I don't expect another movie based off of Ash's adventures in another region. I think this is just something special they are doing because it's the anime's 20th anniversary.