It is quite possible to only open source what legally can be open sourced, and leave the rest closed sourced. This is exactly how it works with operation systems like macOS and even Windows. In time, closed source components can be replaced with open source components, if that is desirable, and by user’s choice.
Regarding rights and licenses, it is just as questionable that all of them were transferable to post-commodore owners in the first place, it can be just as “illegal” for Hyperion...