You'd need a screen able to rotate to allow for different aspect ratios - some pieces use music in portrait mode, some in landscape. The problems I see are: Repeats - You'd need to be able to turn back several pages at once for repeats in the music. Markings - you'd need a very good touchscreen to allow additions to be made during rehearsals. Resolution - Sitting here looking at the sheet music for a rather dense chunk of Rachmaninoff, it's nowhere as easy to read as properly printed sheet music.
It's not a bad idea, it's just that the implementation would be <very> expensive compared to just using the sheet music and any places rich enough to afford it would likely be used by people who play from memory anyway.
That said, as an organist it would be very handy - I frequently need 7 or 8 books during the course of a service and having them scanned in for use in the correct order would be useful.