I don't understand how git is a backend at all; I can manipulate all of the data (text files) without needing git at all. Compare with a wiki, which requires some sort of backend to work with any of its data.
When I use git in this sense, I'm talking mostly about version control and backup.
Heavyweight git backend? Care to expand on that?
You have to add, commit and possibly merge just to add today's agenda or fix a simple typo. Compare that to how easy wikimedia is.