The team started developing it, because they were "dissatisfied with the limitations of all currently available multimedia container formats such as AVI, Ogg or Matroska."
Talking to a lead-developer on LinuxTag in Berlin I have been tought, that most of it is working, and there are only some minor things to fix and decide on, like the FourCC-tag. There is a libnut available already in their SVN-repo, so go and check it out if you want.
So fasten your seatbelts everybody, because this baby is to become the standard when it comes to boxing audio and video data. For more information see: http://www.nut-container.org/