So basically, you want a flip tablet with a phone screen on the outside to use when it's flipped shut. It could even have like a minimalist case around it so it didn't look like stupid. So it looks like one solid thing. Edit, also it opening like a book would appeal to the crowd that hasn't dived into e-books yet because they like that book feel.
That's one possible solution. But the screen would have to be seamless. Not two 7" screens with a fat bezel between. It has to be a phone-size device that becomes a single, seamless 10" display. Also, the 'folded' device can't be thicker than current smartphones, so about 10mm max.
I think many people would trade thiness for more battery life. I'm amazed that a thicker phone with 50% longer up time isn't a part of anyone's line up. Maybe I just know too many nerds that aren't fashion forward and this has been extensively market surveyed. If the nerds would sacrifice thickness for one type of functionality they might sacrifice it for another. All the same,I have a hard time imagining a screen with a seem that would be pleasant to use.