I should read the specs, but since it's such a foundational issue maybe someone who knows could respond briefly? the problem with a flat addressing space is that it requires every intermediate node to have state about every address, or perform a costly discovery mechanism for those it doesn't know about. is there a clever answer to this?
Our default enabled address lookup service is using DNS in a creative way, but we also have a service that is fully peer to peer and is using the mainline DHT, specifically the bep_0044 extension that allows you to store a tiny bit of arbitrary data for an Ed keypair that you control.
https://www.bittorrent.org/beps/bep_0044.html
Some custom transports such as TOR hidden services have a discovery system built in. In these cases we can just use the existing discovery system.
See for example https://github.com/n0-computer/iroh-tor-transport