The rumor mill has been flying for a while, and I think enough has been confirmed for us to say confidently that Apple is definitely going to release a tablet computer in the beginning of 2010. At this point, I believe we can safely say that computer will have a 10-inch electrostatic touch sensitive screen (like the iPhone), and it will most likely have a HSPDA connection to AT&T.

The part that’s unclear, though, is… well… everything else about it.

But here’s my theory:

The MacBook Air was an incredibly cool new addition to Apple’s laptop lineup, but it was really mostly a sales dud by most measures… and I think the only reason for that was that the price was too high. But I believe the Air was merely an interim product — a way to begin recovering some of the costs associated with designing a completely disconnected, paper-thin computer.

Think about it: if you take a paper-thin tablet computer, lose the touch-screen, and add a keyboard… what are you left with, if not a MacBook air?

So what, then, do I expect to see? I think the iTablet (or whatever they choose to call it) will be exactly that: a MacBook Air, sans keyboard. I believe it will fit into a manilla envelope the way the Air does… and I believe that alone will be enough to distinguish it from all the other tablet computer offerings we’ve seen so far. A 10-inch tablet that fits in an envelope is exactly what every traveler on earth wants.

But that’s not enough. OS X has had some excellent handwriting recognition software for quite a while, but it will be better if I don’t need a tablet to enter it. Such features make this an easy Kindle killer. And in fact, if you include a stylus and allow me to write directly on the screen, you might as well go that extra step allow me to use my new iTablet as the world’s best ever replacement for a Wacom tablet.

And if the rumors I’ve heard about it pairing magically with the iMac as a second screen are true, well, how could you not think it’s worth that $799-999 rumored price?