I agree the major problem will be getting people to take part in this - particularly as authors. Whatever we think of the system, there *is* a certain weight attatched to publishing in established journals, and so we are in effect asking authors to give something up in exchange for supplying content for free.
The best way, in my opinion, to get people to do this is to offer something radically different from the norm rather than just a (as yet) less prestigious version of what already exists. It seems to me that there is general dissatisfaction with the current refereeing process, and that some sort of 'active' refereeing could be easily incorporated into the kind of format we're talking about here. I'm thinking of the opportunity to post rebutals to (published?) referee reports, or (more radically) the rubber stamp of 'refereed' only being applied to papers were a (significant) number of people have read and approved of the work.