It would be convenient if such a process could be proven to exist and rigorously described.
Resolving that issue would do a lot to address the OPs concerns. Separately, it would be a strong reason for me to reject moral anti-realism.
What evidence do we have that such convenient extrapolation is actually possible?
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.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.