A quick google showed that I wasn't the only one who had been thinking this: the next generation graphical user interface needs version control inbuilt, so that you are always working with the head of a version tree checked out, and every "Save" is a commit. Applications must allow users to specify commit titles when saving. File managers must allow users to access previous revisions, and rolling back must be possible both at the application and file manager level. But here's what other people are writing.
Examples of how useful version control really is on the normal desktop - in fact, some of the physicists and statisticians in our institute are already using version control for their manuscripts.
Some of the screenshots of Mockup suggest that the developers may have caught on to the idea of version control integrated in the desktop (I looked in their very scarce and sparse specification docs and found nothing).
I can't really talk about Mockup without mentioning the very promising Symphony OS, which once again treats the computer as a device, with user friendliness benefits to boot!
And if you're getting into the looking glass, here's Syllable.