to be completely honest, even I had initially thought it would have been cooler if the e-ink side could do that...until I realised what it would be sacrificing in order to achieve that...

if the device is intended to be used for writing, annotating etc, then having the e-ink side as a touch screen would be a bad idea since it would be really uncomfortable to do these wthout resting your hand on the screen...
Also based on my understanding, a limitation of the 'Electronic Paper' technology itself is the slow refresh rates, so I cant see how a keyboard on that side would be anything but frustrating...

Of course if & when this technology improves its refresh rates, then having that side as a touch-screen with a keyboard (as an option for those who dont intend to use it for writing) would be nice...