No one holds 3.

It is not obvious to me that this is the case.

[edit to expand]: I think that when a cognitivist claims "I'm not a relativist," they need to have a position like 3 to identify as relativism. Perhaps it is an overreach to use 'value system' instead of 'morality' in the description of 3, which was a choice driven more by my allergy to the word 'morality' than to be correct or communicative.

1 is ambiguous; it depends on whether we're speaking "in character" or not. If we are, then it follows from 2 ("there is one objectively measurable value system, namely mine").

One could be certain that God's morality is correct, but be uncertain what God's morality is.

The trouble with Eliezer's "metaethics" sequence is that it's written in character (as a human), and something called "metaethics" shouldn't be.

I agree with this assessment.