First, foldable tablets exist - they are called convertible notebooks. They have a screen and keyboard which can be configured as a laptop or twisted around to make a slate/tablet. Lenovo's X200 is probably the class leader:

http://shop.lenovo.com/SEUILibrary/c...67E79E0E7C9A2D

A dual screen configuration has limited advantages given the current state of technology. What is really needed is a single, foldable screen to reduce the form factor of the device when it is being carried.

I applaud the iPad as a hardware concept but I think that the one thing which would be missed by those who want it as a productivity tool is an active digitizer (ideally combined with a touch screen). With an active digitizer, handwriting becomes possible. PDFs can not only be read but also be annotated. Notes can be taken and stored natively and/or as recognized text.

This is not a new idea. Fujitsu and Motion Computing have produced tablets for years. They now primarily show up in vertical industry devices, especially in health care where the lack of a keyboard allows them to be disinfected. Unfortunately earlier general purpose tablets were limited by weight and processor power (although I still bought one). Those of us who love tablets would like to see Motion Computing resurrect the LS800 with a slimmed down look, Atom CPU, SSD, and 3G:

http://www.pencomputing.com/frames/motion_ls800.html