This is really abuse of public infrastructure if you really want to do this, look at veilid (https://veilid.com/). Veilid provides modern crypto primitives to do this and more importantly the people running the network actually want you to use it like this.
veilid itself basically just provides a p2p backbone (where peers are identified by their public keys) on which you can build other applications. i.e. it's the replacement to the "random public IRC servers" part of this equation, and not the DNS-like system as a whole.
What are assumptions involved for submitting and retrieving node’s IP address with a given public key to a Veilid network? For instance how does new users discover other Veilid nodes. Are those baked in statically? What happens if public IP addresses of the network change?
There's a list of public bootstrap nodes, similar to how Tor bootstraps. Nodes report their own IPs as part of a signed (and timestamped) record, which can change over time. Once you've found one node, you can query it for information about its peers. Because connection information ("dialinfo") is signed, it can be re-shared with other peers.
There's also support for nodes that don't have public IPs at all, which connect to the network via some other node acting as a relay. In this case, they report the relay's node ID.
