Yeah, I mean... I wasn't thinking of the relay operator "provably" not knowing what's getting relayed, but rather just the idea of the operator having a general policy of "not caring."
Discussion
The enclave approach would be close to that, the operator could obviously know what's on the relay, because anyone can query the relay, and the notes are not encrypted. But the op wouldn't be able to do anything with this knowledge, because to change the code of the relay would require breaking the attestation and being booted from protocol compliance. So code-enforced not caring, in a way.
Interesting!