There are plenty of options out there for the software side of displaying (and composing) sheet music digitally. I use Encore, but the market leaders are Sibelius and Finale.
One example where they seem to be trying to bring together the software and the hardware would be:
http://www.musicreader.net/
Given that light needs to be supplied on stages and in orchestra pits, there might be a perceived advantage for backlit devices over eInk, but its certainly a market where a good large size eInk panel at the right price would be really useful.
Note on that MusicReader site that they make the point that annotation is very important for digital music handling. Musos need to make notes during rehearsal.
Graham