NWC wallets don't have static IPs and are behind firewalls too. Clients send ephemeral events as requests to wallet pubkey on some relay, wallet subscribes to requests and replies in a similar way tagging the client pubkey. Same way wallet could talk to a mint doing RPC using ephemeral events. NWS is doing similar thing but with a much more complex setup - enter/exit nodes socks5 etc, and the payload is arbitrary binary data, wheres mint RPC would be much simpler and more structured - wallet just connects to a relay and writes/reads some encrypted events.