The problems as I see it is demand for such an input device is near zero today.
I agree there is little to no demand here right now. But I believe this is because people don't realize the capabilities. If they did I think they would go nuts over this idea.
A good way to think of this is as a SUPER customizable keyboard... I have seen a lot of hype for a keyboard that had customizeable OLED buttons. This touch interface would kick that things butt so bad it's not even funny.
BUT.. on top of that great feature.. you can also use it for tons of other things... AND it allows you to use that extra power it provides on the go as a modular computer to make your home system more powerful by adding multitasking. It takes something that is completely redundant and a luxury on it''s own.. and then by allowing it to work with your computer makes it extremely valuable and useful.
On top of that I don't see a general way to use a tablet with desktop apps.
I have a lot of questions about the logistics of it. How efficient would it be? Would it slow your computer and user interface down?
But if that wasn't an issue I can see COUNTLESS uses for this. Think of it this way... the ONLY use for your normal keyboard would be for text editing. But for EVERYTHING else I could see this tablet interface as being incredibly efficient. Think of when you are using photoshop.. you could use your main monitor for all kinds of reference images or for storing color palettes but do all your image manipulating on your touch screen. Or if you are editing video you would have your playback image all on your main monitor and then use your touch interfacer for all the manipulating and control.
I do think it would take a lot of time to really understand how to use a system like this efficiently and intuitively.. lots and lots of R&D.. but the reason for that is all the capabilities and new possibilities this kind of interface would provide. The possibilities are limitless IMO.
Also.. imagine using MULTIPLE of these Mac tablets in this fashion. You could have all kinds of interactive control mechanism or display mechanism for different element of your computer. The possibilities are truly incredible.. but it requires actually playing with them to explore those possibilities fully I think.
This actually makes me wonder if we will see Apple move away from the iMac design and move to a central appliance like system. So you would have your central brain computer and then multiple modular visual/touch pads people use for monitoring and controlling their computer.. all working together and interacting.. like parts of one large brain.
If you want more capabilities or control you buy another tablet and it grows organically.