well, nothing to joke about, but yeah I think it can work.

The idea is that u use the reputation of the client/author of the event to rate limit. No reputation, no responses.

Now, to get this reputation, you could compute it on your own or use a provider like Vertex.

If you do the latter, than the attacker could make you waste money for ranking throwaway pubkeys. That's were u use IP addresses to rate limit the pubkeys an IP could make you rank.