Nowadays ISPs tend to not give away public IPv4 addresses anymore, but luckily IPv6 adoption keeps increasing.
Recently my ISP stopped providing a free IPv4 address, and my gaming experience with a friend became much worse.
but is was about a dedicated server.
We're both running DST on Linux.
* Host a game where both players have IPv6 connectivity (I have verified it by using a VoIP app the same time, which clearly used IPv6).
* Observe that the traffic actually goes through some Steam relay (it was 184.108.40.206:4379 in my case), with pretty poor connectivity (obviously YMMV, depending on weird routing issues it might even be better, but in my case it was poor)