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.
I've spent a lot of time grooming my idea for a series. I know in my head it won't ever be THE idea that saves Star Trek, but I feel like Sisko in "Far Beyond The Stars", my idea is REAL! And I CREATED IT!
I think if a story were told, the emphasis wouldn't necessarily even have to be "fixing the timeline" as much as it would be "saving the galaxy", and you find out toward the end that what's happening is actually a restoration of the timeline. What this does is gives you at least three very cool things: first, it gives you a new set of characters to explore, do all the good Trek work. Second, it gives you a great overall environment for places and aliens to check out. And lastly, even if just for a few seconds, if done right, it gives you a chance to see the new Kirk and Company in the old school uniforms on the old school bridge of the old school Enterprise, which, despite how contrived that may be, if done right, would be the thing that secretly we all want to see. Just for a second.
If this child of Spock were to be in the new Verse, he would be a refugee. Vulcan is gone. Earth is still there, but Kahn did some damage to Earth. Are the Klingons going to be at war with us in ST3? What's going to happen 100 years from now? 200? If Spock-hura grows up in that universe, would he be more Human than Vulcan instead of the formula of more Vulcan than Human? Would he be emotional? Would he be a warrior, a philosopher, a doctor?