Is that a valid criticism though? I don't run a desktop, just a window manager (scrotwm), and I can still run KDE apps without having to load the entire KDE desktop environment. (Gnome I don't know about, as Slackware doesn't provide Gnome.)
Also, does 'shell' mean something specific to desktop people? What you detail as being the shell, I would call 'desktop'. But I could very well be out of touch with the current lingo.
This approach seems to requires a monolithic application.
I would imagine it could be more open-source-appropriate to separate out the Windows manager (in charge of the details of font and icons) and the shell (the taskbar, start-menu, explorer-type-application etc).
Caveat: I'm working on a shell-like project myself. I suppose I might feel some satisfaction to see Gnome get it wrong but I don't want to see a monolithic system that freezes out alternatives.