It's been a few years since I used Anki, but one of the things that was great was that their decks were public. You could search for and take someone's deck and change it to fit your own needs, which was spectacular. (https://ankiweb.net/shared/decks)
The only downside to that was that for "good" decks that tended to be copied, there wasn't a way to see what was the "best" version of that deck or what was different. For example I had a deck that was copied a couple dozen times, and I'd make improvements to it (such as formatting, adding new questions) and none of those copies would get my updates.
So you could improve on Anki's shared deck feature by treating each deck like a github repo, with branches, pulls, etc.
I have used shared decks a few times, but it hadn't occurred to me that you could apply the open source of branches/pulls etc - interesting idea!
Another thing I'm considering is making the cards sharable as first-class citizens (perhaps under an umbrella category), rather than just dealing with decks. Do you think this would be interesting or do you think decks are an inherently better model?
The only downside to that was that for "good" decks that tended to be copied, there wasn't a way to see what was the "best" version of that deck or what was different. For example I had a deck that was copied a couple dozen times, and I'd make improvements to it (such as formatting, adding new questions) and none of those copies would get my updates.
So you could improve on Anki's shared deck feature by treating each deck like a github repo, with branches, pulls, etc.