In the paper, you say that
However, there is no inherent reason that only one or two experts in a field should determine the validity of a paper, ...
The journals for which I've reviewed explicitly do go out and find experts for the task. They expect the reviews to be informed. Will your contributed reviews be weighted? Are you thinking you'll do some sort of StackExchange thing where contributed reviews percolate to the top, based on others' ratings?
btw: when writing this comment, I wished I could quote directly from the paper by inserting a link so the quote could be read in context. Might be a useful feature.