I personally have a question relevant to this that seems to not have been answered in the previous discussion ref'd by brudgers: what does GNU stand to lose in losing Nano? What does Nano stand to lose by losing the GNU moniker?
I think nano helps fulfill the GNU project's original goal of a flexible OS. I think of emacs and nano as having a similar relationship as wordpad and notepad. That's a bad comparison, but you could say both tools are valid and functional for the purposes they were designed for.
As it stands I think nano is better off hosting development on github or the like. People go to great lengths to install and customize their text editors, so hard core users will seek out the best nano. What sucks is I would be surprised if the next version of OSX includes a non GNU nano, thus fragmenting even further.
This is my 2 cents, and I'm mostly talking through my hat.
With vim/emacs you'll have super opinionated users and they will make sure that they use whichever is the best/most stable version, but in this case I really think politics plays a much bigger part.