In particular, one way (the way?) his metaethics might spit up something that looks a lot like moral realism is if there is strong convergence of values upon agents receiving better information, time enough to work out contradictions in their values, etc. But the "strong convergence of values" thesis hasn't really been argued, so I remain unclear as to why Eliezer finds it plausible.

When you say "agents" here, did you mean to say "psychologically normal humans"? Because the general claim I think Eliezer would reject, based on what he says on No Universally Compelling Arguments. But I do think he would accept the narrower claim about psychologically normal humans, or as he sometimes says "neurologically intact humans." And the argument for that is found in places like The Psychological Unity of Humankind, though I think there's an even better link for it somewhere - I seem to distinctly remember a post where he says something about how you should be very careful about attributing moral disagreements to fundamentally different values.

EDIT: Here is the other highly relevant post I was thinking of.