Like the Batman subset, Superman's would have featured
unique vehicles and playsets. The only ones shown in the
material I received were the Supermobile and Supergirl's
coupe. Of interest is that the Supermobile (which was
based on the comic's version, already having been made
into a toy previously
by Corgi) would have been electronic and
featured a light-up action. And a "deadly nut-net".
This toy did make it all the way to engineering
sample, before being redesigned.
No idea why it was redesigned, or if the word came down
from DC Comics or Kenner. It is interesting that the Kenner
versions of the new designs supplanted the older versions.