I presume it has to be a curated list otherwise spammers would use it to evade blocks. Otherwise why not just use DNS?

Whois would be the choice. DNS’s less glamourous sibling, purpose built for delegated publication of accountability records

Whois isn't curated either.

Neither is nominating a third party for your parking fine.

The point is to get away from centralized gatekeepers, not establish more of them. A hierarchy of disavowal. It’s like cache invalidation for accountability.

If you don’t wanna be held responsible for something, you’d better be prepared to point the finger at someone whois.