And I'm still waiting for USUM to be released independently, since Sun and Moon still has a lot of content to fill in the blanks, and it’s difficult to merge them all into the same chapter in my opinion.
Even if they don’t mention Team Rainbow Rocket or Red and Green in Alola plot, there are still many plots to be completed, example Aether family's following plot, Moon's family background, Anabel and Looker plot, Hau and Guzma plot, Sun and Dollar plot, Guardian deities plot, more Z-move display, Lack-Two's Alola mission, etc. And I think Kusaka will still want all Pokemon to appear, especially those Mythical Pokemon.