Is there another problem besides leaking your IP address(es)? It sure sounds like that could pretty easily be solved by just sending hashes of the IP addresses

Is there another problem besides leaking your IP address(es)? It sure sounds like that could pretty easily be solved by just sending hashes of the IP addresses along with the salt used to make the hashes. Then the receiver could compare it's own hash and know if it's on the same network. I suppose there might be a problem with IPv4 since there are so few IP addresses, so you'd still be vulnerable to targeted attacks, but it would solve the ad network problem. Am I missing something or just underestimating the usefulness of hashing?