Eeeeehhhh, I dunno. I think it's really very obvious what direction Mac OS X is going, and with iOS and the iPhone/iPad/iPod Touch and the Magic Mouse and Magic Trackpad, Apple is clearly getting people used to the idea of touch-screen devices.
Steve had said many times that he didn't want there to have to be anything between the user and the software - no mouse, no keyboard, no stylus. He just wanted you to use your fingers to touch the screen, the most natural interface of all.
OS X 10.7 has tons and tons of design cues from iOS. They've made a multi-touch track pad just for their desktops now so you can use multitouch gestures with OS X. Hackers found code referring to an iOS version of Expose. It's pretty clear that the two computer types - the desktop and the tablet - are going to merge in the future. In my opinion it'll be the very near future, too.
I do like your idea of a large iPad with a stand, though. If they did something that was essentially a Cinema Display that you could take off the stand and carry around with you, bringing the desktop, laptop and tablet into one device, that'd be pretty incredible. It'd be a Cintiq but with an actual computer in it, not just the screen. I think that's a little further off than the iMac Touch though. It'd have to be very thin and light, but powerful, and I'm not up to speed on current tech by any means but I don't think they'd be able to do something like that any time soon.
Thinking about it though, that's a very niche product that would likely only appeal to artists. I think it's much, much more likely for Apple to continue fusing OS X and iOS into one OS, and dropping it into an iMac with a new hinge and touch screen, then it would be to sell people on an iPad with a 15-inch screen, let alone some kind of artist's dream device of a 20-plus-inch touch screen canvas that can be put on a easel on their desk.