I'm working on p2p application, all these NAT-PMP and UPNP NAT traversal scenarios are so unpleasant to deal with. Any thoughts on when IPv6 will become commonly used?
It will be a LONG time before you can drop IPv4 support, if that's what you're getting at. Also, don't be so sure there won't be NAT in IPv6 too. A lot of people want to use IPv6 the same way they use IPv4, and that means isolated internal networks with NAT to the public side. At first it was looking like there weren't going to be any implementations of IPv6 NAT, but now I believe there are, so you can't even count on the disappearance of NAT (still, it should be 1-to-1 NAT, which is a little easier to deal with than n-to-1 port overloading). Even without NAT people still want stateful firewalls, so you still have to poke holes in those for P2P.