I think the audience will start picking up E-readers the moment they start selling them for under 200.
You know that article about Esquire's 75 edition? They had a small, seemingly pretty tough plastic e-ink screen.
When they'll have a screen like that, and a simple tab on the bottom with some buttons and battery,that's probably when they'll start selling!
BTW, have you seen how fast this screen refreshes?:
Edit: How do I successfully embed a Youtube video?