I wonder if good VCS could solve this problem. For instance, if he documented each step with comments/commits in the code as well as he did for this blog post,

I wonder if good VCS could solve this problem. For instance, if he documented each step with comments/commits in the code as well as he did for this blog post, it would be easy to go back and see not only why he did what he did, but the much more readable (albeit less performant) original code. It seems like most git guis are pretty commit-focused. I'm not sure of any way to do it in the command line (though it must be possible) but it would be nice to highlight a section of code in your IDE and have git give you a history of just those lines (or that function) as far back as you want to go.