I absolutelly love this idea!!
I just think that using | would be a bit strange, maybe hard to understand, and most possibly won't be found by someone who doesn't read the whole help file (and let's be honest: who does?)
I think that the -tab- option is better. Right now, it gets the path of the whole file on the editbox, but i see no reason why it shoudn't do what you said in the first post. Notice that if one wanted to have the directory of the file, one could just do ctrl + rightArrow, and to copy the path of the file itself, one could do arrowDown and then ctrl-c. Thus, i don't think that using tab to autocomplete files is very useful right now.
On the other hand, if we wanted the functionality refered on this post to be available for both files and folders (since one could, for example, apply the "zip" action to a whole directory), then, as tab is VERY useful with folders, it could not be used for this.
Also, another reason why i'm a bit relunctant is that | is only accessible through shift-\ in my keyboard.