His? His what?
LOL I think he meant that from what we know, and in appearance, he seems to be mostly vulcan body-wise but it's also true that vulcans and humans share a lot of similarities in terms of both of them being 'humanoid species', to begin with, so there might be many different aspects of his biology that weren't addressed and that are either human or a mix of the two, but it may be hard to see where the 'non human' starts due to the existing similarities between these species.
Generally speaking, I think that for narrative purposes Spock's hybrid nature is mostly showed in a simplified way in that they use his appearance to represent his vulcan side, and his feelings to represent the human one. But even that is incorrect because I actually think his most passionate and violent feelings might come from his vulcan side, and perhaps in some instances it's his control that is human and can't compensate. Would be great if the new movies added more layers to this.
But I digress, the fact remains (my original point) that Spock is still a hybrid and he inherited genes from his human parent too. He's mixed. This can't be ignored because it means that regardless if he makes vulcan babies with a vulcan or a human, he will always father kids that have some human in them. If the vulcans were to consider his and Uhura kids not useful as vulcans because of their human side, I doubt their opinion would drastically change if he had kids with a vulcan because those wouldn't be 'pure vulcans' either. In either case, Spock wouldn't be their no.1 candidate.
This was only one of the points I made though. I still think that, regardless, all the vulcans would get asked to contribute but they'd find a more efficient and logical way to save their race than waiting for survivors to procreate the old fashioned way. Even if they don't have to wait every 7 years (you all, even DC Fontana was annoyed by some fans' misinterpretation of pon farr being assumed as the ONLY time they have sex)
eta: vulcans are compatible with humans so I think that 'anatomically' there wouldn't be a lot of surprises for Amanda and Uhura beyond maybe there being a fascinating shade of green somewhere. I guess the vulcans aren't for humans who want to try something truly different (btw, anyone got a clue about what was the purpose of Syl's head being like that in Beyond?)
Japan tour start today (lets hope they like bikes and Elysium style space stations)
https://twitter.com/TrekCore/status/787981979312648192
still annoyed by how cool and professional the asian posters look compared to what the rest of us got.