I think the multipurpose device is mainly a marketing device that allows manufacturer to sell their products for higher prices. People end up buying several multi-purpose devices that they use for specialized purposes.
I remember 20 years ago, the future of home entertainment was supposed to be a multi-purpose device that would be a TV, computer and gaming platform. I had trouble believing this at the time.
And now, what do we have? Gaming platforms and computers that can show movies. How many of these multi-purpose devices does every one of us own? And how many uses does each one of them serve?
Nowadays it's practically impossible to buy a mobile phone that doesn't take photos, except for the very low end of the market. Have sales of digital cameras plunged because of that? No, because most people still want a camera, even if they occasionally use their mobile phones to take quick photos.
The main beneficiaries of multi-purpose gizmos are the manufacturers, who get us to buy more expensive gadgets with more non-essential functionalities.
I'm sure e-readers will get more functionalities. Will we really benefit from them? Maybe, marginally. Will the manufaturers benefit? Probably, but on the other hand they are creating more pressure to make devices that do everything, which increases costs. Competition nowadays seem to be more and more on non-essential and eventually costly improvements.
Just my 2 cents