It's funny, cause when people were doing the Dex count it didn't seem like there was room for new UB's after burst and assembly, and we still got adhesive. I think there is one more new UB left...after all we have three new UB's and four Ultra Reacon members that we've seen. I think it's likely each one of them have there own new UB.
I really hope that there's more, just to make exploring certain UB's worlds more exciting. It would be cool if there are some more that you can actually breed, that maybe even have evolutions, and function more like regular Pokémon. I really like the whole idea of UB's and their designs, but you can't really breed and raise them, which I love the most about Pokémon! It would be cool if after this game they got ret-conned to have genders and be breedable. I hate having too many legendaries because you catch them already at high levels and can't breed and raise them.
I'm gonna repost this:
We know for sure that between Lunala and Necrozma in the new alola dex there are 9 spots for UBs but now we have 10 UBs.
We know some UBs are seen before national dex: Burst; Assembly; Guzzlord; Adhesive. This leaves 5 free spots that can be occupied by Nihilego/Pheromosa/Buzzwole/Kartana/Celeestela/Xurkitree or be completly new UBs, leaving all the others to post game.
Please notice that we have seen all the Ultra Worlds for Nihilego/Pheromosa/Buzzwole/Kartana/Celeestela/Xurkitree while we haven't see the Ultra Worlds for the UBs which are seen before National Dex so maybe we will catch these last on Alola and all the others in their USpaces ---> we may not see all Ultra spaces.