Things I've noticed so far, not mentioned above. (I think)
1) Project Settings>Appearance>Preview is not displaying any previews.
2). Command clicking the title of a window is not producing the file ladder as it should (standard Mac behavior)
I'm not an expert on this file type, but would a progressive need to load progressively on an object as it would on a web page? If so, I can see how this might cause problems in a 3D scene.