In the panel on the right (is there a name for this section?), it would be nice to have a directory listing. Kind of like Open File, but the directory listing is there in a panel. Then have it so all you have to do is double-click on a file name to load it.
Then, what would be slick, is if you have files open from different directories, the directory listing would change with whichever file (tab) you have open.
Attached is what it looks like with EditPlus.