I'm pretty sure the Xbone doesn't use UPnP (From reading what the network guys at Microsoft have said, and from the fact that my Xbone doesn't ask for any ports to be opened), apparently it only had around a 25% success rate on the 360 so they didn't bother with it on the One (Considering the Xbone is designed for IPv6 first, falling back to Teredo, so you either don't have a NAT, or rely on NAT traversal anyway)
Nah it doesn't, it uses the methods Teredo uses. I find it quite puzzling that the built a system around IPv6 and using Teredo for that. Although Teredo does help with NATs as it uses various traversal techniques. I feel like IPv6 won't properly kick off in the X1s life time.