alt Hacker NewsIpv4 does NOT have this problem. The typical setup is always NAT for ipv4 lan, so external address can be changed with minimal disruption.
All ipv4 apps that require hole punching assume they will need to "discover" the external address anyways, for every new p2p connection.
In contrast to the vast majority of ipv6 apps which assume their ipv6 address is identical to external ipv6 address, as this is(was) the main marketing point of ipv6 - directly addressable end points.
"Directly addressable endpoints" is how the Internet is supposed to work. It's how it did work for anyone who grew up with the 90's Internet.
NAT is a hack that let us get 30+ more years out of IPv4, nothing more. Sadly, we now have a generation of engineers who thinks NAT is normal.