For opening large files, it is fairly pointless to wait hours in order to view the header of a 5gb video, or finding out the schema name of a 50gb database dump, or trying to edit 3 lines on a 6gb xml stream. What I am suggesting here have almost never been done by other editors before. What you do is specify a window within a large file that you want to edit. This is to say you let the program know where you want to start opening the file, and for how many bytes do you want the edit window to be. When you save, the beginning and the ending of the file are appended to your editing window. Many database programs use this technique, and i think it can be a valuable addition to EmEdit
Yes, I have been already thinking about this feature!