I think the whole idea of Spock's child by either Saavik or Uhura is just fine--depending upon what you do with it.
Somehow restoring one or the other timeline seems to me the kind of story that would only appeal to certain hardcore fans, leaving everyone else wondering what the hell is going on? Essentially it reads like a (possibly very good) piece of fan fiction rather than something intended for a general audience (although to be sure the two are not mutually exclusive).
What kind of person is this child? Where did they call home? How do they feel about Starfleet, the Federation, their parents? Describe their personality in some way and you might get my interest.
Conversely you might ask--which Vulcan or seeming Vulcan we've met already might actually be this offspring? Admiral Savar, for example? Sokanna? Might Vorick be Spock's grandson?