I was actually meaning to make a thread on this today--I theorize that Super Saiyan White villain or whatever Toriyama mentioned in an interview, is actually going to be Super Saiyan (God?) Black Goku. His hair will turn white with the transformation...
I think that White Super Saiyan is going to reveal some sort of origin to the Super Saiyan transformation. There has to be a reason Red, Blue, White, and Yellow for that matter are introduced as super saiyan variants. Double4Anime theorized Cabba will unlock Super Saiyan Green, although his theory was pretty much arbitrary and on a whim, I think there could be something more to the different hair colors. Blue could just be the natural Deity transformation for the Saiyans of universe 7.
EDIT: For those who are unaware, an interview was released about a month and a half ago. This article was discussing why Toriyama did not make Super Saiyan Blue, Super Saiyan White. His answer to why Goku and Vegeta will never get White hair (In canon) is that it is because that power up is reserved for the next/future villain. So I theorize Super Saiyan White is going to be either A. Black Goku going SSJ or B. SSJG