I am sure you have watched the video preview of Windows 8. If you haven't, shame on you, it will turn out to be a crucial moment in the history of computing... Ok, ok, I'll add it below here. Watch it and then come back.
Now, tell me what you felt and what you remember if you close your eyes.
Exactly, it is all smooth and nice and wow until you get around minute 3:00. He opens Excel, Windows creeps in from below and you think "oh, s**t, that's ugly, I want to go back to the other interface!".
I think that reaction is telling. We want good UIs, we want the new touch interface, we are tired of windows, we like tiles and things that magically update themselves. However, Microsoft needs to be backward compatible and - as Michael points out - they were successful once with launching Windows 3.1 while having the ugly DOS window in the background. Maybe they can do it again.
The problem is that we have moved on. Mentally. We, as users of mobile devices and tablets. We like what we have now, we do not want to go back. The paradigm has shifted, a new era has begun, mobile is becoming desktop. The desktop is tired, it needs to move, to become mobile.
One thing in particular kills me in that video. He says: "Because it is a PC, it has a file system". I think it tells everything. It is a PC, it has a file system, it must have a file system, right? Or it would not be a PC!
I do not think so.
The file system is dead.
Think about it. It is the biggest change introduced by Apple with iOS. There is no file system. Documents live within applications. Pictures live within the picture app. Videos within the video app. Books within iBooks. You can move stuff around (from Mail to iBooks) but there is no concept of file system.
I know you know what a file system is. But ask your parents. Did they ever understood the concept. Fully? Do they ever created folders within folders? Do they get the tree? No. It is complicated. It is not intuitive.
Actually, it is not necessary at all. It is a complication of the metaphor. One we can live without.
Of course you'll have a file system underneath. I am not advocating killing the OS file system. We geeks will use it to move stuff around, but the end users do not need it.
Eventually, they will not need the old Windows UI either.