If I am not mistaken, what you want is to unstage hunks interactively? I thought git reset -p does exactly that. Its prompt message is even exactly like Unstage this hunk?
Also from the manual:
This means that git reset -p is the opposite of git add -p, i.e. you
can use it to selectively reset hunks. See the “Interactive Mode”
section of git-add(1) to learn how to operate the –patch mode.