Having an interview of the current architect for the visual editor would be interesting for sure. I'm pretty sure Andrew Ozz has been handling the tinymce integration for at least a year or so. Other than Ryan Boren and Matt M. I don't know who else has worked on it.

There are a few third party things like phpmailer in WordPress, but I would point to TinyMCE as the most complicated to integrate since it involves php, javascript, and html. Along with dealing with a third party developer (Moxiecode) it has to make coding interesting.