I am not sure how many sales are made per month with Sublime Text now, but I imagine it has decreased significantly in the last year or two. I still think ST, being native rather than running in a WebKit window, has a great potential for being the most popular graphical text editor, but it will continue to dwindle if others are not allowed to work on it. Currently, many developers are wary of using a proprietary text editor since there are many great alternatives, but the few of us ST users left have a special attachment for the software regardless of the shrinking userbase. The custom cross-platform UI framework could possibly be used for other project applications after being made a standalone library by contributers.
I believe the GNU General Public License would be ideal for Sublime Text, as it disallows nonfree derivatives.