Regarding multi-purpose devices - don't forget that CPUs are getting more "abilities" too.
Take a look at
this CPU - unless I'm mistaken, that should be the one inside the Kobo Wifi. At least it's the same family.
Sooner or later you probably can't even buy a CPU that doesn't have MP3 and whatever else integrated.
Of course, you can ignore that and don't use it. But I doubt that would be cost-efficient, as you're still paying for them.
(Also of course, it's a chicken/egg situation. But once in motion, I doubt it will be stopped any time soon. Perhaps other architectures are different, but then I suppose there's a reason why ARM is widely used.)
Personally, I welcome multi-purpose devices - as long as they have a dedicated use and the rest is mere "extra".
I wouldn't mind not carrying an MP3 player for example.
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Re: Keyboards - there've been rollable keyboards too. Maybe that would be useful? Bluetooth or whatever, so you can place wherever you have room, and foldable/rollable to store it.
Here's an example.
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[edit] Ah drat, might as well say a word on topic: eReaders are cheaper and smaller, no wonder they sell better.