This isn't that hard. It's even easier now that many people have IPv6. IPv6 still usually requires rendezvous due to stateful fireballing but it otherwise behav

This isn't that hard. It's even easier now that many people have IPv6. IPv6 still usually requires rendezvous due to stateful fireballing but it otherwise behaves like 1:1 NAT. (IPv6 is occasionally deployed with NAT, but in that case it is 1:1 NAT without port remapping which is also P2P-friendly.)