There are lots of reasons to discount the threat as not imminent, like your other point to me that targeting a carrier group is not an easy thing. True, but IMHO there's a lot of puckering going on as the number of years before we really gave to worry has shortened considerably. There is no joy to be had.
I think we're in basic agreement over the fact that we need to question our assumptions. I tend to be skeptical that the Chinese would give the keys to their nuke designs to the NK's. I don't know anyone else that would do it either. This is not to say that the Chinese aren't taking political advantage at our discomfort.
I think that basically China wants to control the territory of NK, but recognizes that the Kim-regime is not long for this world. If Kim gets a bomb - it vastly complicates things for the Chinese too.
My guess is that Kim is a 'Dead-Man walking'. China is going to take him out via assassination/coup. I think there has already been a few attempts (witness the expoding trains).