(disclaimer: I created https://pagekite.net/ which is one of localtunnel's competitors)
And while a bit toung in cheek, i'm not too aware of this whole ip address scarcity thing. I've got a decent chunk of a /29, if you could use a /48 or ten for your local networks just ask! Or would it be tough to squeeze down to only 18,446,744,073,709,551,616 local addresses?
Tools like PageKite and localtunnel are completely in line with that philosophy, nothing is exposed to the outside world until you explicitly request it and then only the named service you chose (as opposed to whatever is on the port or god forbid everything listening on a particular IP). I personally feel more secure temporarily exposing a server using PageKite than I would if my router had been reconfigured to always allow traffic through on particular ports - it's a lot easier to turn PageKite off than it is to go reconfigure my router every time I am done testing.
Convenient security is good security, because it is more likely to be used correctly.
IPv6... well, good luck with that. :-) Aside from how few western ISPs offer IPv6 service, consider the fact that the majority of our devices are mobile these days. My laptop changes networks and IPs many times a day and I still like being able to run a visible server on it. Configuring plain IPv4 or IPv6 to do that elegantly is decidedly nontrivial.