> As to porting anything else, why would anyone feel compelled to do that?

Because the porter wants the software on his preferred platform, for instance :-)

> if members of our development team believe that part of the MUI4 repository that was
> used contained work from developers other than Stuntz, then it seems quite likely.

Even then it's still a difference whether the source code was obtained legally (from Stuntz, but with non-Stuntz code, so Maus/Böckelmann have been acting in good faith) or illegally.