IP privacy. I've talked about this before, but this is here for completeness.

If you do something like outbox model, clients will be connecting to whatever servers the protocol (other people's events) is telling them to use, such as perhaps honeypot.nsa.gov. And this happens automatically without you typing it in and choosing it. BTW this also happens if I go to a website and that website tells my browser to pull a javascript library from honeypot.nsa.gov... it would happen automatically, I didn't type it in, and I'm not even aware that it happened.

So IP privacy is a thing we care about.

IP privacy, if achieved at the IP layer by a solution that is decoupled from the rest of the solution here, is IMHO the better outcome. Tangling together IP privacy solution (garlic/onion/leek routing) with a social protocol just locks you into a possibly inferior IP privacy solution. I think VPNs and Tor are 'ok' but maybe we will see a new better IP privacy solution come along.

Sometimes you can solve IP privacy 'good enough' by having a node act as a proxy, and so at the social application layer that kind of architecture should be possible, but that doesn't need to be in scope when defining a client-server protocol.