Grades with comments may be set fo each version (in other words - for each editing) of any page in the wiki. To grade book must go final grade, combined by one from a list of methotds, like in
Workshop (it is best but hard to develop) or
Quiz (in simple way)...
May be will be good, if for one grade-item (page version) make possibility to set more then one grade - and not only by teacher. it is like in forum posts, that have list of grades from peoples.
And good idea - have place to write descriptions for each setted grade, like in assignment.
May be (if forum engine will be transformed to set of functions, that can be used in other
activities to make embedded internal forums) don't make any self implementation of grades system and make attached forum for each page and each page version with using forum\s grading with self-maded grade summing.