Why do you need to invoke acausal trade if your selling point is "I've proven that I can pre-commit to some arbitrary X"?

I don't think Eliezer would argue that the AI is going to turn itself "friendly", that would amount to suicide and therefore wouldn't be instrumental. But you are right, I don't think the experiment makes much sense. I just tried to pick the most convincing argument that might still be considered a realistic possibility given my best guess about the mindset and framework of beliefs of the people involved in the "experiment".