It seems nobody has been able to answer this for the last 15 years. A quick glance at
https://sites.google.com/site/freeamiga/ shows just what a spectacle this is and how much illicit activity it has been surrounded by.
The only party enforcing the copyright is Cloanto, but they say they don't know who owns the Kickstart, and don't seem to be interested in finding out. They don't even seem to know who they got their own license from.
Cloanto are also the only party who profits from selling the Kickstart and Workbench software. What a coincidence.
If someone did own the rights and cared about protecting them then they would've come forward and settled this many years ago, and I more believe the theory that the rights perished with the liquidation of Commodore.
If someone actually still own the rights then it would most likely be Amiga Inc. or Hyperion Entertainment, but if even Amiga Inc. themselves can't or refuse to give any answers then it just further supports the theory that the rights are lost and that the software is in the PD.
If you're able to find any answers it would be great if you could let us know here as well.
