If someone is running a relay, they can see your IP address and client credentials when you use the relay, not far from doxxing you. This will be important for those who want anonymous pseudonyms (once clients handle multiple identities, this will become more prevalent) but use the same client with their real identity attached.

obvious solution but challenging: tor enabled relays

social trust solution: have relays disclose what they log and why. bonus: add a web of trust (WoT) metric for relay operations

technical solution: a code signed open source relay that doesn't log environment variables (a malicious person could put a logging proxy in front of that)