At the moment the technology is moving fast enough that I wouldn't want it built into a keyboard console, especially for acoustic instruments where the possibility of following what you're doing to do the page turns at the right time is pretty low. Most music stands will hold a tablet pretty well.

There is a degree to which mass-produced woodpulp paper (rather than parchment or vellum) and engraved printing (rather than copying out parts painstakingly by hand) were necessary pre-requisites for the Romantic-era growth of the size of orchestras and the length of symphonies (in the way that the same things plus the cast-iron piano frame and rise of the middle class were prerequisites to piano music getting really popular and even profitable); if you're getting the whole lot printed then you may as well go big and long. (There are other factors too, like people who weren't the landed aristocracy starting to go to concerts qua concerts where the entire point was to listen to the music, and larger halls, and so on and so forth; I am not a historian of music and am probably leaving out or eliding a bunch of stuff.)

What we're missing in this conversation is not "Can we get e-paper to do what deadtree paper does, only a little bit better?" but rather "what can tablets/e-paper do that would be totally impossible with deadtree paper?" -- things like having a computer program that generates (playable!) sheet music on the fly based on the movements of people in the audience, for example. (That would be kindof evil for anyone who doesn't like sight-reading, but, hey.)

(And now I really do need to learn how to program. Damnit.)