Now, however, even that seems to have been found. A museum director in Buenos Aires discovered that a copy of the tapes in their possession was, in fact, a copy of the original "long" version of the film, as seen at the original showings in 1927.
Needless to say, this really excites me. Metropolis is one of my favorite films of all time (Hell, I've got 3 different versions here), so to see that it might finally be fully restored is a pretty big thing to me.