http://pcottle.github.io/learnGitBranching/
If you take that approach and update with precise but plain english vernacular (redundant?) and domain specific examples, then you are halfway there to making it understandable by regular people.
The most important thing to help people really get it is to promote small commits to their work. The real value of git only makes sense when you start making small commits. Having worked as an editor in a past life, having something like cherry-pick and interactive rebase would have been most dope. In a way, maybe editors are the best audience for driving adoptions among writers in general. For professional editors, version control is a painkiller. For writers, it is a painkiller if the writer is an obsessive editor. For those who write and commit once, but don't go back and review commits and refactor, it doesn't provide much value.
Think about how Apple Time Machine made a stab at operating system backups and snapshotting. Was it perfect? No. But it was a step in the right direction.
Loren and others may not solve all the problems right out the gate, but they will lay the groundwork for new approaches to teaching version control to writers and other audiences.