As others have said I don't see the point if it is not more portable- and unless it fits in your pocket (which means a 5" size) a 7 inch size brings nothing new to the table. I would rather see a higher rez display and less weight.
Yes...
I want more portability than an iPad.
I want something you can hold in one hand comfortably.
I want to thumb type.
But I want a size that you can comfortably read pdfs/books/.
I'm heading for mid-age and reading pdfs on my iPod Touch is frustrating and getting difficult.
The 7" inch is perfect--the size of a paperback (remember those?).
It will fit in a murse/purse/jacket pocket.
I never go out without some kind of bag, so I don't need something that fits in my back pocket.