Gonna be honest, at this moment in time, new Alolan forms are highly unlikely. Around this time for SM, they started revealing the second stages of the starters and introduced the Festival Plaza - all the Alolan forms were all done by then, as they were one of the hottest new things that this gen would bring to the table. Now they seem to be focusing on the USUM-exclusive stuff, such as Necrozma's forms, the photo club, and surfing on Mantine. It seems too late to start putting in Alola forms now, and knowing how much GF loves Kanto, they probably won't do the same for other regions.
Also, the poster that was leaked a few weeks ago, featuring artwork of Lillie clutching a Pokeball, Hau looking more determined and what appear to be Aether grunts wearing different suits hasn't really been touched on yet by GF. There's been a lot of speculation that Lillie succeeds in her role in being a trainer and that you get to battle her, but this pic here suggests that early-game, she's still the same as she was in SM, right down to the hairstyle and her trying to get Nebby in the bag:
Also, nothing has been said about Hau. Like I said earlier, his new artwork shows him looking less carefree and shows a more determined side to him. This alone suggests that we might be getting something really dark happening over the plot of USUM, to the point where these can be considered the darkest Pokemon games, possibly even rivalling Majora's Mask in tone.
One final thing I'd like to bring up is something that was tapped into during the SM datamine but hasn't been revisited since: connectivity with Pokemon GO. During the datamine and the resulting text dump, this was discovered, and subsequently leaked everywhere:
Oddly enough, nothing has been said about connecting to GO from SM. It was speculated that this was how you would get the standard forms of Alolan Pokemon into the game, like Meowth and Raichu, but even if was going to happen, one has to highlight the problem of
how to connect your phone with your 3DS. A similar thing was possible in Japanese copies of Crystal, but with select phones and Gameboy Colors. There's also the issue of how to transfer if you're signed up with a Google account and not through the PTC, because it seems to be geared towards PTC players. Maybe GO connectivity can be added into USUM, considering that Gen III seems to be on the horizon.
