That's not easily solved at all. That's an incredibly complex system you're proposing. IMO the solution is simpler. Heavily rate limit the creation of namespac

That's not easily solved at all. That's an incredibly complex system you're proposing. IMO the solution is simpler. Heavily rate limit the creation of namespaces. That's less viable for crate names, but it should be very uncommon to create more than a few namespaces. You could give people a low number that aren't rate limited, like 5, and then rate limit them to 2 a day afterwards. They can then publish unlimited crates under those namespaces.