I was in the Apple Store last Thursday and got to try the iPad Pro and pen in person.
One of the demos they have is a program called forScore.
It's basically a pdf reader with pen annotation capability.
You can download a pdf score from the internet, and use the apple pencil to add your own notations in a variety of colors and line styles--basically what I do now with pencils and highlighters on my paper scores.
There are additional apps that allow a "director" to sync the score on a whole orchestra of iPads.
Perhaps some of you know about this program, or similar, but it was my first time seeing it up close,
although I've seen some bands using tablets instead of sheet music.
The advantage of the iPro, of course, is the pen. And the screen size.
And since it will take ANY pdf, it should work just as well for alternative notation.
Not as nice as the Windows Surface StaffPad score editor, though!
Joe Austin