First, I doubt that Apple, with a touch interface for the iPhone so new that they still haven't figured out the fundamental cut-and-paste, has come up with an appropriate interface for whole-computer touch system.
And I don't see the value of going the traditional bolt-on approach (unchanged OS with pen-interface added) since six years of tablets from Windows suggests that no one really wants a tablet. They're too expensive for the power, too heavy for their size, and the interface is too kludgy compared to normal desktop keyboard & mouse.
I'd love to be wrong on this. I've been dreaming of the ideal scientists tablet computer for a decade now. I think such a tool with appropriate software could revolutionize the way students, scientists and engineers work. Or at least solve many practical problems. But the software and hardware doesn't exist, and I don't see any signs of it coming.
(caveat: a super-iPhone tablet I'd believe. Something like an 8" ultra portable with 960x540 screen -- 50% of 1080p -- with the iPhone OS X, not desktop OS X. That seems much more likely than a MacBook Tablet with traditional OS X.)
I gotcha Dave. Hence the X-Files reference since we agree that this is pretty unlikely. I don't doubt that Apple will eventually make some kind of tablet, but when they do I expect it to be unlike anything anyone else is making and have its fair share of things that people find infuriating, only to be cured over 4 convenient yearly revs =)
Of course, I want a desktop Mac that doesnt cost $3k more than I want this, but YCAGWYW, especially not from Apple.