I've recently merged the latest stellarium to my dev branch and moved to the May 2013 version of W Steinicke's NGC catalogue. I have been thinking about the best way for users to make use of it, bearing in mind the non-GPL license.
I considered a plug-in, which would ask for confirmation from the user before downloading the catalogue for the first time. On the other hand, the nebula class is a core part of the code and may not be easy to override in a plug-in.
Otherwise I was thinking to add the option to the config dialog, but it's already quite full. So I'd want to add a new tab, again the program would ask the user to accept the non-commercial usage license (which I need to agree with the author of the catalogue, Wolfgang Steinicke).
Any comments welcome.