Yeah, but chain operations become extremely expensive over time.

> If all I have is a pubkey, how do I find the corresponding IP?

There are many ways, but you basically would have a boostrap IP that can download NIP-65-like events of other relays. We could even use WoT to ask your friend's client to become the Bootstrap relay. Once you have a list of available options saved locally, you can easily get updated records by just querying a few of them. And if they go offline, you update the list with new ones. As long as you know the IP of a single relay, you can get all the others.