@Scrabbler
Your post reminded me of several related things from which I was able to jump to a conclusion ... of sorts.
First, people inherently interact differently with desktop & laptop computers vs tablets and smartphones. The form factor of the latter makes them more suitable for a touch-centric interface because you're physically holding them. With desktops and laptops, however, it's somewhat awkward to be touching and pushing on the screen all the time. (Though you'd never think that, judging by all the fingerprint smudges people get on their screens in our office.)
And since direct (touch) and indirect (via input devices) interaction are not entirely similar, forcing either onto a device designed for the other would seem less than optimal. Not very Apple-like.
But ... then I remember that Apple was granted a patent for a device that operates one way (say, like OSX) when the display is vertical and another (say, like iOS) when the display is horizontal. The same could be triggered when the device (an iPad) was nestled into a keyboard/trackpad dock, thus essentially converting it to a laptop. (It could be a desktop ... but the screen isn't that big, which to me is the most notable difference -- aside from portability -- of a laptop vs desktop.)
Now, when you think about it, the big difference between a tablet and a laptop is basically the touch screen ... and that keyboard thing (forgetting issues like Flash ... which is less and less of an issue each day). If Apple were to equip MacBooks with touchscreens, they'd essentially be like a big iPad that was permanently mounted to a foldable keyboard dock.
So, how tough would this be to do? Well, when Apple intro'd the iPhone several years ago, they explained that iOS is essentially OSX Lite with a different UI. I don't know how accurate that it is, but it seems logical. Assuming it's true, then it should be fairly trivial to have one OS (iOSX?) with two UIs that it switches in and out of as appropriate. Of course, it would be best if they functioned similarly enough all the time that the only things that change are natural changes that don't confuse a user. For example, the touchscreen might still function perfectly well in vertical orientation ... even though people might do most of their work with a keyboard and mouse/trackpad then ... because you don't want it being non-responsive if someone does reach out and touch the screen.
As someone else pointed out, iOS might need to be opened up a bit to allow installation of programs from USB drives or other sources. But supposedly Apple is working on better sandboxing technology that might make that possible without raising security issues.
It seems not only plausible to me that Apple might eventually merge the two platforms, it seems likely. I wouldn't be surprised at all if, in a year or two, MacBooks are much more like iPads running a hybrid OS. That would allow Apple to actually eliminate the MacBook product line, leaving the ultra-portable iPhone/iPod Touch; the tablet iPad with optional keyboard/trackpad dock; and the Mac desktops, all running a shared OS.
. Also, merging the two systems would mean that iOS would have a "visible" file system structure, Xcode, etc. (developing apps on a touch device is not something I'm looking forward to). An alternative would be to have the dev tools and infrastructure remote, but you'd still have to use some touch approach to development. Really? 
