It's obvious - both the prime timeline and the JJtimeline would merge, creating an alternate 1985 where Biff has become rich and married Marty McFly's mother.
Given how protective Spock Prime is over his secrets, I doubt it would happen. Although, if Trek XIII really is supposed to be the last of the Abramsverse series, I could see Spock Prime being on his deathbead and he trasnfers his katra over to Quinto Spock.