Possibility of "writing" on the paper is missing
Grading an exam with more complicated, less predictable, answers (mathematical proofs) many of my graders expressed the desire to be able to mark something on the student's paper. This is not to write long texts, but to be able to precisely show where the errors are. It might thus be sufficient, and perhaps even preferable, if just the possibility to put a fixed mark (red X) on the work, as opposed to the possibility of writing with the mouse was implemented.