You'd have to invent this one at least, as it currently doesn't exist. As the DNS server operator, you can view all my DNS queries. In a zero-trust environment where I don't trust you not to log all user queries and forwards them to the NSA, you'd need to use homomorphic encryption and create a DNS client and server than can do a lookup, without you, the DNS server operator, from finding out what the DNS lookup was of.

https://github.com/menonsamir/spiral-rs claims to have implemented this at a level that's practical for real world applications, with a demo for a wikipedia server, but it's far too slow, as demoed, for use as DNS server.

Now, the fact of the matter is that you can map my account ID back to the IP I'm connecting from, but with very limited way to map from my IP to my identity protects that in many ways, but data-mining at scale, knowing how many users connecting to one proxy server from city X, would be worth something to advertising and related companies who are more interested in large habits of users. If it turns out no one uses the pirate bay anymore, but use torrent site XYZ, I know where I'd place my advertising dollars for, say, a VPN product.

This is on the extreme end, but you asked for a fun challenge! :)