I want to make a couple of points.
1. Emergence of Alternative UIs
2. Desktop as Possible Alternative UI, so that Dock and Traditional OS environment is only left for apps
3. Need for Such a Situation
1. Apple has introduced two shipping alternative UIs: Front Row and Dashboard, where the user leaves all interactivity with the normal OS environment. And it has introduced Time Machine where the user in a way leaves the traditional OS environment (although is still working with files etc).
2. The current method for dealing with files is the Finder, Desktop, Open and Save dialogue boxes, and the trash can in the dock. It is confusing for people like my grandmother who I help on the phone with her iMac quite often. Maybe the desktop will become an "alternative UI" like the ones I previously mentioned. It might be a three dimensional wooden table top, upon which you interact with files, see your disks, and so forth. It would be invoked in some similar manner to Dashboard and would eliminate the use of the Finder. The traditional OS would become just another UI, one that has a dock and applications, but no finder or trash on the dock. That would be handled by the Desktop UI.
3. This would greatly simplify the use of a computer I believe. You have a desktop where all your stuff is, then you have Dashboard where your widgets are, and you have the traditional OS environment where you use your Apps, and finally Front Row for using your media.
Don't be too harsh with this wild idea, it's 2 AM and I'm a bit punchy.