In the small scale your rationalization is logical, however in the big picture you're going to end up with teaching people to make useless commits. As long as this is true of ungit, it is a project i will have to vehemently recommend against in any circumstance.

What ungit should do is the same thing as git gui: When you go to make a commit, you can view diffs of your files and select single lines to be added to your next commit.

Edit: I've created an issue for this: https://github.com/FredrikNoren/ungit/issues/98