This idea is similar but certainly not the same as the Peer Graded Assignment module (see http://moodle.org/mod/forum/discuss.php?d=679) I am thinking of rehashing that module and developing a "Student Graded Assignment" module where the teacher sets up a set of files (probably from previous cohorts) and the students grade them. The teacher then grades the students' grading preformance. That's probably further from what you have in mind!
I think The Peer Graded Assignment module has all the elements you require it may be just a matter of re-packaging them. It's very definitely phased in that there's a set-up phase, a submission phase, a (peer) graded phase and then a teacher grading phase. There's TWO deadlines as opposed to the normal one. I suspect that what you are looking for is a continuous creative curve
There are a number of questions which spring to mind. Do all the students grade all the submissions? Is there a growing pool of submissions? When a student comes along do they get allocated a random sample to grade? Is there a fixed deadline or is it a moveable feast? Is this really an assignment? Is a student expected to add to the pool of submissions?
I suspect the answers to all these questions are both Yes and No! What would be really useful is a scenerio of what might happen in practise over time in one of these Presentation areas, that could be coded. Like what is the starting point, what's happening in the middle and when does it end, and if it doesn't end how is the pool of submissions managed.