Nice writeup and the policy is a step in the right direction. I suspect simple rate-limit measures like this will be a big improvement.

I suspect a logical conclusion Arxiv and elsewhere may be an identity management system with an aggressive filter, and shared blacklists. I suspect that classifying people as spam/slop-submitters, then banning them (or whatever identity they used; name, email, name + organization etc), applying incremental rate limits over the general one, may be required.