Dangerously approaches the kind of small universe and fanwank stuff that drives away new viewers (and is the stuff of fan films), but if they could do it in a way where it doesn't matter that you know the back story (see: the easter eggs in Beyond) then I would not oppose it, and probably would drool over it. I think it would be easier to use minor characters that we don't have a lot of expectations about how they "really" are. If indeed the Number One is THE Number One, that's a good example. Maybe characters that were TOS one-offs: Daystrom, Boyce, Finney, etc. But not characters like Mudd, as much as I'd love it.