Annotation systems - most recently hypothes.is - have tried to catch on in the education technolopgy space, but despite considerable pushing they haven't, really. Why not? I'll go with Nate Angell's three reasons listed here (paraphrased): annotation is attempting to displace existing practices; annotation is only now starting to reduce friction of use; and annotation would need to be an essential part of people’s required activities. The thing is, the interface on a computer is very different - annotation by keyboard is very different from annotation by pen. So I don't see these three things ever being eliminated.