Win 8 is an awesome OS that is better than Win 7 in every way EXCEPT when in mouse and keyboard mode. The lousiness of the mouse and keyboard mode may be a matter of personal opinion, but given the poor adaption rate of Win 8 and the popularity of Start 8, its the majority opinion.
If they take Win 8, give it a good start menu, throw in windowed metro apps for good measure, then I think they will have a major winner.
However, this is Microsoft. They are going to screw it up. My prediction for how MS screws up Win9 is:
1. The start menu sucks. They design it to be flat and every app gets installed in it, or something along those lines.
2. Subscription based model. That will kill it for me in an instant.
Im not sure how else they could ruin it, but I expect there are many more ways. They ability of MS to screw something up is surpassed only by the governments ability to screw something up.