KDE, Canonical, and GNOME have all made this huge push into stupid design decisions lately. Canonical with Ubuntu Phone/Tablet and Mir, GNOME with GNOME 3 and treating the desktop like a tablet, Mozilla with FirefoxOS, and KDE with this sort of stuff.
You know what I want out of an open source desktop? A DESKTOP! Seriously. I need a good desktop environment for my COMPUTER where I do actual work. I can't write code on a tablet. I can't write papers on a tablet. I can't do serious design work (anywhere, because I'm not a designer, but specifically also not on a tablet).
If I want to use a tablet, I want to use it to play games and watch movies, and Ubuntu/KDE/GNOME tablets aren't going to have Civilization Revolution, Ticket to Ride, Netflix, or Amazon Instant Video any time soon, so any tablet running those operating systems is going to be just a really crippled computer and a useless tablet.