git add -i is a good idea, but the interface is just /atrocious/ - confusing, poorly worded, visually unattractive and hard to read (dark blue text is not very user friendly on a black background).
I guess it's a matter of taste. I would find the context switching between the shell and the GUI more jarring than the usability of `git add -i`. Also, shell colours can be adjusted.
But in the end it's good to have multiple options.