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E-ink is not practical either. The power needs to be boosted to ~100v (power hungry), each key would need a separate screen, and would have to be manufactured to be tiny. E-ink alone is expensive, probably even more so than OLED, much less color e-ink! Which is still in prototypes for many companies. Color e-ink will not hit mainstream consumers for a good 5 years.

Either way, you are looking at huge manufacturing costs, poor durability, and sucky key quality.

Oh, and future kindle? Uses a light buide printed on top of the screen. To do this with keys, the LEDs will have to be on top of the keys, which again makes backlighting very difficult.
 
Wouldn't it be much easier to get keyboard covers with the letters on top. Just rip em off and put a different one on straightaway.
 
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