Some twenty years ago I came across an article on a steel frame possibly 753 custom built by a German frame builder. Besides having a very tight geometry, the frame hada rear ward facing track style dropouts. The derailer mount could possibly have been welded on. The rational being that once positioned, the spring of the derailer actually pulled the wheel into place.
It seemed a novel idea at that time and I wonder why the trend did not catch on. Anyone else heard of this?