There is a way of testing metaethical theories, which is to compare their predictions or suggestions again common first-level ethical intuitions. It isnt watertight as the recalcitrant meatethicist can always say that the intuitions are wrong... anyway, trying it out n EY-metaethics, as you have stated it, doesn't wash too well, since there is an implication that those who value murder should murder, those who value paperclips should maximise paperclips, etc.
Some will recognise that as a form of the well known and widely rejected theory of ethical egoism.
OTOH, you may not have presented the theory correctly. For instance, the "Coherent" in CEV may be important. EY may have the get-out that murderers and clippies don't have enough coherence in their values to count as moral.
I don't think the coherence part is particularly relevant here.
Consider two people, you (Peter) and me (Matt). Suppose I prefer to be able to murder people and you prefer that no one ever be murdered. Suppose I have the opportunity to murder someone (call him John) without getting caught or causing any other relevant positive or negative consequences (both under your preferences and mine). What should I do? Well, I should_Matt murder John. My preferences say "yay murder" and there are no downsides, so I should_Matt go ahead with it. But I should_...
In You Provably Can't Trust Yourself, Eliezer tried to figured out why his audience didn't understand his meta-ethics sequence even after they had followed him through philosophy of language and quantum physics. Meta-ethics is my specialty, and I can't figure out what Eliezer's meta-ethical position is. And at least at this point, professionals like Robin Hanson and Toby Ord couldn't figure it out, either.
Part of the problem is that because Eliezer has gotten little value from professional philosophy, he writes about morality in a highly idiosyncratic way, using terms that would require reading hundreds of posts to understand. I might understand Eliezer's meta-ethics better if he would just cough up his positions on standard meta-ethical debates like cognitivism, motivation, the sources of normativity, moral epistemology, and so on. Nick Beckstead recently told me he thinks Eliezer's meta-ethical views are similar to those of Michael Smith, but I'm not seeing it.
If you think you can help me (and others) understand Eliezer's meta-ethical theory, please leave a comment!
Update: This comment by Richard Chappell made sense of Eliezer's meta-ethics for me.