Let's spin up a distributed hash table that maps public keys to the relays they use. Make sure it's accessible via tor and only the user who owns the pubkey can update their record in the table. This is better than NIP-05 because it isn't tied to the centralized DNS system, and better than NIP-02 contact lists because it works for people who don't use any of the same relays you do.
Discussion
Not a bad idea. I am skeptical of DHTs, but happy to be proven wrong. Please build it. Ideally inject it into an existing client and make it work. There will be a bounty for sure.