The thing about those TabletPC's is that they seem more like regular Windows notebooks with some extra pen input features slapped on. And since they're more expensive, they will then only sell into niche markets. The big driver seems to be the pen input thing to differentiate the form factor. Bad choice...
IF Apple does a tablet type device, I think they will have a completely different design goal. It's not going to be for vertical industries, it will be for regular consumers (but of course can be used at work and home.) And they won't start with a Windows XP notebook and go from there, they will start with a blank piece of paper. The basic idea I think is this-
1. Cheaper, smaller, lighter than a notebook but offering 95% of the same functionality that people actually use in their notebooks.
2. Designed from the ground up to go beyond basic PIM tasks, which is all the small PDA form factor is really effective at. I mean there are some people who do Office and email and web and programming on a PocketPC or Palm PDA, but I don't think most people are interested in that, the screen size and interface is way too confining.
Basically a roughly 5 x 7 tablet is what I'm thinking, in iPod/iBook white. In that size you can have a nice 800 x 600 screen and a good battery. Some of the random features that I was thinking about-
1. Some sort of 'Smart Agent' type software interface, to make the user experience really nice. Not just Zen of Palm, but something people will really enjoy using. Power users could still use faster shortcuts for doing stuff.
2. Thin client (already discussed here). Connect to your Mac or to iMac easily and seamelsssly. This would also give media-center Mac control.
3. Dedicated hardware for multimedia processing (faster and saves battery vs. everything being done by the CPU). The Sony CLIE TH55 is a great example, it does great movies and music with only a 123 MHz CPU.
4. Maybe a 20-30GB hard drive for storage, with a super-stripped OSX that runs in RAM (really doesn't have to be OSX based though. Having a Aqua-ish interface is more important.)
5. Works just like an iPod, with the touchscreen being used as a scrollwheel. Connects to a Mac/PC just like an iPod. Can stream music wirelessly (to and from) via Airport Express, etc.
6. Dock connnector for compatibility w/ many iPod peripherals, including the iPod Photo Camera connector
7. Wifi/IR/BT built in (of course), as well as ethernet port for wired access.
8. Support for Apple wireless keyboard and mouse, as well as 3rd party devices (Stowaway BT keyboard, Palm Wireless keyboard)
9. Streaming radio and podcasts
10. Simpler version of iPhoto, or maybe just iPod Photo functionality
11. Built in iChat with voice and maybe low-res video chat
12. Email, RSS, web (duh)
13. Skype Client
14. Some iWork or MS Office compatibility (like a version of Dataviz Docs To Go)
15. Dashboard widgets for all sorts of extended functions (in some ways they could be cooler here than on a Mac.)
16. Spotlight-like functions, with OS indexing. Automatic journaling of what you do, so you can go back to any date and see what you did.
17. Comes with a nice-looking 'man bag' to address portability (since it can't fit in your pocket.)
Most of these are very Mac OSX or iPod features (except for the man bag), but realistically don't need a G5 and Tiger to pull off (no ripple widget effect though!) But they can leverage both the Mac and iPod as much as possible here. So you can leverage a lot of this cool Apple software functionality in a small tight package. It's a lot of features, but not necessarily a lot of expensive hardware.
My brainstorm is somewhat half-assed, as I have been mainly brainstorming functionality and features, rather that starting from a end user perspective. But that would take too long, and I'm not a designer anyway..
This could come out at maybe $649 or so (probably $699 but can't be more.) But the cost would also drop over time, in a couple of years this would be a $299 device. At that point I think it could become pretty compelling for more widespread penetration.
Also, the lower the price point, the closer this becomes to actually being the 'video iPod' that we've all been speculating about.