The implementation of the git-diff highlighter (a.k.a. git gutter) in git.kak is good, but putting git update-diff on a NormalIdle hook, so that the gutter stays up to date as the buffer is edited, can make the editor sluggish. I edited the implementation to make it asynchronous, to avoid slowing down the editor as much: GitHub - evannjohnson/git-async.kak
I’ve been using it for a week and it seems to be working smoothly, but I haven’t done any testing on different machines. Let me know if you have questions or run into issues with it!