I know it's one hell of a stretch, but it would be nice if USM got 20 or 30 more new pokemon. Just a nice addition.
It is funny you should mention the 20 number. I know PokeJungle isn't always the best source but in this case I am more referring to the game journalist Laura Dale.
Firstly she wasn't the one who said Pokemon Stars (which I took to be it's code name and she also stated that it was). Would be on the switch and secondly she also said that there might be 20 new ones.
Seeing how Itech Post also picked up this part of the story (the 20 new Pokemon bit) and seeing how there was as Serebii themselves found out a technical error. Putting the TBA of the switch on the official US and UM page. Which has since been removed. And Laura got the info from a ask me anything where the code name of Pokemon Stars, which we now know to be US and UM.
I think it is safe to say that there is still a chance that this 20 figure could still be correct as in my mind it is independent of the whole Switch incident.
If we are also to assume the Alternate story might take place in the future. depending how far into the future could also give an explanation as to why any new Alolan forms were not seen in the previous Sun and Moon.
So personally I think the new Pokemon will be Pokemon from previous generations not found in the original Sun and Moon games as well as new Alolan forms. I highly doubt they will be completely new Pokemon from scratch though.
Maybe new hope for water Arcanine
Edit:
Regional variants are distinct Pokémon with different appearances, stats, typings and movepools relative to their counterparts - despite the relationship, they aren't just forms. Entirely new Pokémon and new Alolan variants are prohibitive for the same reason.
Different appearances yes. But same 3d skeleton model to work with. Plus for them to get these games ready for announcement about 7 months after the release of the Current Sun and Moon they would have to have been working on these ones along side them.