There'll probably be a shift due to mainstream demand. But I think there will still be enough people out there who will appreciate a nice slow eInk device
So even if eInk is peaking right now, I think that this peak will persist (meaning that I still would buy an eInk instead of a backlit LCD). Theres just something about ereaders that a tablet won't cut. My Laptop and cell phone play mp3s, still I prefer my dedicated mp3-player.
Don't get me wrong. I'm not against video. But an eInk like they are now just resembles books better for me than something like the ipad. So I love the "slowness" of the reader but prefer the small size and additional functionality over pbooks.