So if an Idealized Aris (IA) knows the exact height of Everest, and the Base Aris doesn't, does that mean the only options are:
IA does not make use of the words "height" and "Everest".
IA makes use of the words and means the same thing as I do, so he can only know the height of Everest if I already know the height of Everest.
IA's referents for the words "height" and "Everest" are different from BA's. Therefore height and Everest doesn't mean what I think it means.
Somewhere your logic has holes in it.
It's not true that if IA and BA mean the same things by "height" and "Everest", IA can only know the height of Everest if BA already knows the height of Everest. My 2 does not use the same (erroneous) logic.
I think I've found a better argument that Eliezer's meta-ethics is wrong. The advantage of this argument is that it doesn't depend on the specifics of Eliezer's notions of extrapolation or coherence.
Eliezer says that when he uses words like "moral", "right", and "should", he's referring to properties of a specific computation. That computation is essentially an idealized version of himself (e.g., with additional resources and safeguards). We can ask: does Idealized Eliezer (IE) make use of words like "moral", "right", and "should"? If so, what does IE mean by them? Does he mean the same things as Base Eliezer (BE)? None of the possible answers are satisfactory, which implies that Eliezer is probably wrong about what he means by those words.
1. IE does not make use of those words. But this is intuitively implausible.
2. IE makes use of those words and means the same things as BE. But this introduces a vicious circle. If IE tries to determine whether "Eliezer should save person X" is true, he will notice that it's true if he thinks it's true, leading to Löb-style problems.
3. IE's meanings for those words are different from BE's. But knowing that, BE ought to conclude that his meta-ethics is wrong and morality doesn't mean what he thinks it means.