This is indeed a trivial XEP, for Audio, it can help know if the client is behind a NAT, yes. Does it says it is the same NAT to be used when user places a Voice Call over UDP? Absolutely not. But I'm quite convinced that it can give hints.
But I still see a point on it, which is when we may have deployment of XMPP Servers, which can have provide Hints about NAT, without STUN requirement. (Yes, we all know STUN is more reliable for UDP). The goal for me is not to have the retrieve IP as Jingle Candidate, but how will I describe my local address type. This is specially useful for gateway between Jingle and SIP for instance. Where u can have a hint, that the call should be proxies as the client knows for sure he is behind a NAT. (Considering 99% of all SIP deployments does not support ICE properly) Unfortunately we still need to think about SIP deployment compatibility.
