I would argue that there is still plenty of room to make tablets not like the iPad, and the plain black slate monolith is not the only form:
The lope-sided design of Sony Tablet S makes sense if you think about the ergonomics of a book while you are holding it.
Also another thing comes to mind is the lost Courier’s dual screen layout, if not because manufacturers are too cheap to put two screens in one device.
Or how about putting speakers around the rim, giving it a meshed appearance? That would produce much better sound.
Technologies like Philips’ ambient “leaked” light may also help legibility and distinct the tablet from the mass.
Or how about color e-ink? Mirasol? Pixel Qi?
So many ideas but too few brave souls indeed.