Totally agree, i hope unity will shine, my adding more and more goodies. On my tablet i would really want to have a full linux, if that is at all possible.
Was Unity specifically designed for a tablet? Does the window system have multitouch support? Accelerometer support? Do any of the applications themselves support multitouch and accelerometers?
Though, in a couple of years, who's to say that Ubuntu won't be able to run on most devices? Maybe there are challanges, but I doubt that it would be impossible. It's just a matter of time and maturity.
I think people are already asking for one user environment across devices, so I bet it's something they might have in mind.