>>33329763>>33329786We legitimately have no idea yet. There appear to be things that are the same but there are also things that are definitely changed, like where you initially get the starters, but at the same time even Platinum changed that. The only thing they've shown us so far is the 1 minute trailer today, and the cutscenes for the legendaries with Necrozma armor on them.
It's probably a better idea to wait and see if they're super different from SM before getting just US or UM, but they might be completely different after all.
I doubt it, though. 