I'd ask what problem we're trying to solve. I think desktops should be out of the way. I don't really use "a desktop" for anything. I just need a way to launch and switch between applications, and that's a solved problem in my opinion.
The problem though is getting rid of the desktop would not go down well with the majority. you'd need a way of proving that you can still make multi tasking painless. Currently a desktop environment means I can resize and arrange windows to allow me to work with multiple apps.
One idea is have some sort intelligent system for deciding how much screen real estate is needed for each app and how they can be grouped and arranged into sensible workspaces.