The natural use for this would be a laptop with a netbook form factor and 21" roll-out screen.
Now that 3G is ubiquitous and cheap in the developing world (more so than in the US or Europe even), this is the final piece in the puzzle for truly portable dev on the road. A machine the size of a paperback that you can do real work on while hopping chicken buses across South America.
To me, a roll-out screen implies a certain amount of non-rigidness (unless you're going to make the device weigh 10lbs.). Seems like a 21" screen on a chicken bus (or subway, or plane, etc.) wouldn't be such a great fit.
Now that 3G is ubiquitous and cheap in the developing world (more so than in the US or Europe even), this is the final piece in the puzzle for truly portable dev on the road. A machine the size of a paperback that you can do real work on while hopping chicken buses across South America.