I guess a good thing (?) about the whole Ultra Sun and Moon situation is that GF will reveal everything in the promo campaign.

They revealed everything for ORAS and SM and since this is just an upgrade they need to focus on showing new stuff/forms/features. I doubt we will get a trailer every 2-3 weeks as it was for SM but obviously once a month they might show what they have. Then we will know if its worth buying or not.

Realistic expectations
>New Alola forms (ORAS has new megas), probably for Kanto and maybe Johto mons
>new trials (the Lycanroc cutscene seems like a Totem animation)
>some region redecorating (maybe they'll open up the golf course)
>new exclusive z moves (obviously)
>some story changes and new cutscenes (allthough i doubt we will get a whole new story, its been only a year)
>maybe few more old characters in the battle tree
>move tutors
>walking animations (they had them ready for SM anyway)
>extra old legends in the post game (I would expect the ones that werent in ORAS so Xerneas, Yveltal, Mewtow and birds)

Is that enough for you to buy it?