Old topic, but still relevant (as I don't think this has yet been implemented).
When the OP suggested moving a specific *directory* to the end of the disk, it was quite obvious to me they meant the files contained *IN* that directory, not the file table entry as you commented.
Take for example my brother's computer (or the in-laws system even). I had copied over much of the contents of their previous computer to a sub-directory on the system. This way if there were some files that were needed but not obviously placed, they could be recovered from that back-up copy. But as they are an 'archive' of the old system, they aren't going to be changing (if they were going to be updated/edited, they'd either copy or move the file to the active documents directory, etc). As they are no longer actively changing, no sense in keeping them in the middle of files being actively changed ("actively changing" can include OS and application files as well as data). The same goes for various video files. If they're bulky and unchanging, might as well get them out of the area of most activity.