Google announced Google Wave today, an "attempt to imagine what email would be like if it were invented today". It has a robust collaboration infrastructure strongly grounded in distributed systems theory. If I were (re)starting the OLPC project today, this is certainly what I'd base Sugar on — with as much corporate support from Google as possible, since the project is strongest when it has strong allies.
I believe you could make each school server into a Wave Provider, using the Network Principles I drafted while employed at OLPC to ensure appropriate DNS-style naming. Any document format based on XML can be made collaborative using the Operational Transform mechanism. The journal's large scale history/versioning mechanism could be based on the same principles, as So6/LibreSource demonstrated. And the UI demonstrated in the keynote (which I haven't even fully watched yet) would be an exciting way to implement the neglected Bulletin Board feature.
It would be an exciting start to the Sugar project! But given the existing code base, is there now too much bathwater around the baby to consider swapping the child out?