I'm pretty sure it's the first step of many towards an actual unified account system.
This update happens next month (?)
end of 1st quarter may see expansion on the idea, and maybe by end of 2014 we will have all the pieces in place to actually call it a Unified NNID Account.
Nintendo is a turtle in this game. They dance to their own beat, and usually several songs behind, but they'll get there eventually. Just can't say if all of us will still be around to care by the time they do...