Nobody is gonna be using a quantum computer to “crack email hashes” of Plex users in a few years… I’m not even sure there is a speedup to hash cracking with quantum computers.
But depending on the hashing algorithm used, it’s likely pretty easy to crack hashes of email addresses today with a normal computer. They’re not particularly high entropy.
I have no skin in this game, but IPs are definitely not anonymous data. Also there is a lot of great info out there about de-anonymizing seemingly random data. Interestingly enough, this is similar to the Netflix prize dataset that was one of the more famous ones. Maybe a good introduction to that would be https://www.schneier.com/blog/archives/2007/12/anonymity_and_t_2.html