I think that workflow might work if people (maintainers) are submitting HTML or README.md's or whatever for their docs. But for 'collaboration' with visitors/readers, it would need t be simple. I personally wouldn't want to pull out the command line and git clone, edit, commit, push just to get some tweaks or examples added to the docs unless it was a project I contributed to regularly.

Another thing that might come in handy is something like code review tools that let you add comments for specific line numbers -- but for sections/paragraphs of the documentation. This could also serve as a revision history discussion as well as questions/comments on the information