I would honestly love to see a ground-up rebuild, but not the kind that would probably happen. OSX is getting creaky; it seems like it's had an increasing number of integral bugs lately, and the "redesign" that came with Yosemite felt more like a rushed coat of paint than a substantial rethink of the UX. Here's what I'd like to see: a fresh desktop OS that actually innovates in the space. Desktop UX innovation has sl…
The real questions are whether or not present-day Apple administration has enough vision to (want to) carry out an OS migration and, as you mention, whether or not the vision is any good.