That's a good question to ask. My opinion: nothing, basically, on either side. You could argue that being an official GNU project gives nano a level of legitimacy and carries with it an implied quality level. I wonder if nano would ship by default on basically every *nix distribution without the help of GNU. Last I checked, it was nano, not emacs that comes preinstalled on an Ubuntu image.

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.