Erikstormtrooper said:

If they shot Empire of Dreams on 16mm film, wouldn't an HD version be possible?

It would be, but I can pretty much guarantee you they didn't shoot in 16mm. For one, it wouldn't be practical or cost-effective, and number two it really doesn't look like 16mm. Also, since a lot of the doc is not original footage (talking heads) but b-roll from other sources it would depend on the source quality of those (dailies, footage seen in other docs like Making of SW and never-before-seen clips, newsreel footage, miscellaneous, etc.).

Even if the raw footage of the interviews was shot in 16mm--which it likely wasn't--the master was probably a standard-def video one, probably on something like DVCPRO or Digibeta.