If Apple logged (incoming IP from user, outgoing port to exit node) pairs for each session, and the exit node logged all requests, this should be sufficient to associate all requests with a given user IP, right? Or am I misunderstanding you?

I wouldn’t expect them to log it, personally, I think that can only lead to headaches down the line. My reason for responding is just that I disagree that there is no way for another party to associate all requests even if Apple & exit node both fully cooperate and keep logs.