[Sophira]

While individual clients may not be easily identifiable, there's still a measure of identification that could be made, if you were to configure the public key DNS server to send a different (but persistent) public key to each IP address which asks for the DNS record. (Probably an ISP's caching nameserver.)

You can't tell how many people are going to be covered by that public key, but you could probably make educated guesses, or combine this with other metadata.