I see no reason to restrict our preference extrapolation to presently-existing humans. CEV should extrapolate from all preferences, which includes the preferences of all sentient beings, present and future. Any attempt to place boundaries on this require justification.
Edit: You might say, "Why not also include rocks in our consideration?" Simple: rocks don't have preferences. Sentient beings (including many non-human animals) have preferences.
What if the majority of sentient beings are ants and beetles?
If it's worth saying, but not worth its own post, even in Discussion, it goes here.