Well, I for one don't want a desktop UI on tablets, I don't think I'd be able to use that. Maybe it's not a problem for people with good eyesight and normal muscle control, but my not-so-good eyesight and muscle coordination problems would probably make it very difficult for me if Apple were to simply slap OS X on a tablet.
Micrsoft spent more than a decade trying to cram desktop UI onto tablets, and it never really took off. Then Apple came along and showed that a tablet with a UI designed for tablets can sell very well, even if it's not as powerful or feature-rich as a full desktop computer. I expect that eventually, Apple will keep adding more features to iOS until it is as powerful as OS X -- and maybe by that time the two will merge into a single OS. But I don't expect them to just slap OS X as it is now onto a tablet, and I'd be disappointed if they did that.