It's just struck me that there might be a tension between the coherence (C) and the extrapolated (E) part of CEV. One reason that CEV might work is that the mindspace of humanity isn't that large - humans are pretty close to each other, in comparison to the space of possible minds. But this is far more true in every day decisions than in large scale ones.
Take a fundamentalist Christian, a total utilitarian, a strong Marxist, an extreme libertarian, and a couple more stereotypes that fit your fancy. What can their ideology tell us about their everyday activities? Well, very little. Those people could be rude, polite, arrogant, compassionate, etc... and their ideology is a very weak indication of that. Different ideologies and moral systems seem to mandate almost identical everyday and personal interactions (this is in itself very interesting, and causes me to see many systems of moralities as formal justifications of what people/society find "moral" anyway).
But now let's more to a more distant - "far" - level. How will these people vote in elections? Will they donate to charity, and if so, which ones? If they were given power (via wealth or position in some political or other organisation), how are they likely to use that power? Now their ideology is much more informative. Though it's not fully determinative, we would start to question the label if their actions at this level seemed out of synch. A Marxist that donated to a Conservative party, for instance, would give us pause, and we'd want to understand the apparent contradiction.
Let's move up yet another level. How would they design or change the universe if they had complete power? What is their ideal plan for the long term? At this level, we're entirely in far mode, and we would expect that their vastly divergent ideologies would be the most informative piece of information about their moral preferences. Details about their character and personalities, which loomed so large at the everyday level, will now be of far lesser relevance. This is because their large scale ideals are not tempered by reality and by human interactions, but exist in a pristine state in their minds, changing little if at all. And in almost every case, the world they imagine as their paradise will be literal hell for the others (and quite possibly for themselves).
To summarise: the human mindspace is much narrower in near mode than in far mode.
And what about CEV? Well, CEV is what we would be "if we knew more, thought faster, were more the people we wished we were, had grown up farther together". The "were more the people we wished we were" is going to be dominated by the highly divergent far mode thinking. The "had grown up farther together" clause attempts to mesh these divergences, but that simply obscures the difficulty involved. The more we extrapolate, the harder coherence becomes.
It strikes me that there is a strong order-of-operations issue here. I'm not a fan of CEV, but it seems it would be much better to construct, first, the coherent volition of humanity, and only then to extrapolate it.