Hum… not much, maybe something with <kbd>Super</kbd>, but e.g. GNOME-Shell does use some of that (<kbd>Super+LMB</kbd> and <kbd>Super+Shift+LBM</kbd> -- actually the same as my WM but with <kbd>Super</kbd> instead of <kbd>Alt</kbd>). <kbd>Super+Ctrl</kbd>? Meh, not enough modifiers.