I think that NAT is a major reason why P2P and self hosting failed to take off in any significant way. I think that the internet would have been a wildly different place were IPv6 widespread in the early '00s.
I wonder why NAT hole punching techniques never took off much with P2P, it seems like with enough work getting around NAT most of the time would be possible.
Good, reliable ways to do hole punching were not available until relatively late (STUN, ICE) and were somewhat finicky for a long time, especially on crappy routers.
Also, multiple levels of nat are unfortunately common and make STUN unreliable