After seeing what's happening with Jasper, I believe Steven Universe Future will not have actual villain. In the promo and intro, they really make Jasper look like a villain, but in the first episode, we see she's more of a jaded hermit, and a possible ally. She doesn't seem interested in fighting the new order, which sinks a lot of theories which had her as the main antagonist for the series.
With that in mind, the fact that White also appears in the intro may mean that rather than the figures in the intro being enemies Steven has to fight, they are instead the "triggers" for his new power. When he encounters them in the show, they are going to push him to the point where his anger explodes and he fights with his diamond powers. Characters like White, the new fusion and the two Lapises are going to fight him and make him lose his composure, but it will be due to Steven' feelings of helplessness, and not some evil, overarching plot.