Resolving that issue is part of the overall goal of the SI, and a huge project. I'm also a moral anti-realist, by the way. CEV should be starter-insensitive w/ respect to humans from different time periods. My reasons for why I think that this is achievable in principle would be a whole post.
I'd be very interested in a theory that harmonized CEV with moral anti-realism.
And you seem to believe in a very strong form of extrapolation. I'm personally skeptical that CEV(modern-humanity) would output anything, while you assert CEV(modern-humanity) = CEV(ancient Greece). Surely you don't think CEV(Clippy) = CEV(humanity).
minor terminology note: I've always used CEV and (moral) extrapolation interchangeably. If there's a reason I shouldn't do that, I'd appreciate an explanatory pointer.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.