End user residential connections usually need a DynDNS as there's no guarantee you'll get the same IP for any foreseeable time period. So dynDNS could be bundled with hole punching. (It just allocates a port on the CGNAT, due to cost concerns I'm guessing these are rather dumb TCP/UDP devices, so almost anything will work through them.)

Of course it's a lot messier than getting a static private address allocated.