Hi,
I was pretty impressed by Atom’s git-time-machine package (https://atom.io/packages/git-time-machine). Of course, that is not possible in ST. But here is something that might be possible. When the curser is at a line or selection that includes changes compared to the last git commit, a tooltip shows the modifications compared to the previous version with colored text for additions and deletions. So a tooltip would basically show this (but only color the added part green, not the entire line)
Just an idea. I might give it a shot over the next months but I thought I share if someone wants to implement it.