[saurik]

Does the CGNAT setup you contend with not support NAT-PMP/PCP? (To me that is the reasonable solution to the problem you cite, not IPv6, and I have been thinking it is already widely deployed... just not adopted by developers for some reason.)

[tenebrisalietum]

I don't contend with CGNAT, thankfully, but no one ever moves from IPv4 then everyone's going to eventually be behind a CGNAT at some point.

I don't know too much about NAT-PMP/PCP - so I'm looking into it.