iMac with detachable screen
The Register ran a feature on the new iMac in the Summer, where they claimed it would have a detachable touch sensitive screen that could be used for Web surfing. It would communicate wirelessly with the iMac base station, and since OS X is a properly layered OS, the base station would run the kernel and low level processes, leaving the detatchable screen to run Quartz - the graphics layer. This neat approach would mean you could use the screen unit to control several different Macs remotely.
Such a device would look very similar to this unit, although I would expect the CD/DVD drive to be on the base station to enable the tablet to be as slim and lightweight as possible.
Clearly you'd want to build handwriting recognition into the unit - this is where Newton comes in useful for once 😉
This this device would rely on OS X, it would have to run OS X as default, OS 9 would only be accessible via Classic.
If they release this device, it truely will be revolutionary, and very difficult for Windows PC manufacturers to copy.