Hey /vp/. I’ve come across a decent bit of info regarding USUM.
The new facility in the festival plaza is a secret base kind of thing that lets you design your own gym/trial.
Double z-moves is story only, there’s a new smaller island named Makini thats similar to the post game island in platinum. There’s no new battle facility, but you can change your challenge type in the battle tree to be more like the battle factory/hall/castle/arcade. Select characters from previous games return as the “frontier brains”. For instance, colress is the head of the factory, Wallace is the head of the hall, Caitlin is the head of the palace, and clemont is the head of the arcade.
There is one more ultra beast, and it is the evolution of UB sticky, codenamed UB sealant. It is poison/ground type.
A few more legendaries can be found using the new ride function, including mewtwo, the weather trio, deoxys, the creation trio(including arceus), heatran, xerneas, yveltal and zygarde 10%(note, the zygarde cell quest is still a thing). None of these pokemon are shiny locked.
Last but not least, there are in fact new alolan forms, and they are the legendary birds. Moltres becomes ghost/flying, zapdos becomes steel/flying, and articuno becomes water/flying. These pokemon can be found in a post game sidequest regarding the aether foundation and them experimenting with “artificial symbiosis”.
As far as I know this is everything that they have not revealed so far, so make of it what you will. I am willing to answer and questions you may have.