I'd call that size finally large enough. I have yet to pick up an e-ink reader and the 5"-6" standard is one (minor) reason. The Trade Paperback form factor (similar to my old Nook Color) looks just about right.
The price... well, one could pick up a tablet of similar size and PPI for not much more, but it still seems just about right for the combination of features. It ticks off all my boxes (display quality, front light, microSD) except for a hackable Android OS, but it's looking less and less likely that B&N will release another generation of e-ink Nooks stepping up the PPI