That sounds like a personal goal? I'm not sure I see any necessary reason that linux exist solely in either category (open-source true purpose, or popular desktop). Did I miss the argument?
I guess I'm obliquely commenting that keeping the project small and in the hands of open-source developers, may be pointless. Otherwise, why agonize over what others are doing with it? Either we want others to use the open-source version too so its a popular desktop with lots of attention, or we don't and becoming a popular desktop with lots of attention doesn't affect those open-source die-hards at all. Either way, a successful project becomes popular on a lot of desktops.