The IP is dead, there is no more Amiga IP, it's well past 17 years on everything. The Trademark is legally registered in the US and EU, but outside of those places, especially non-Madrid protocol countries the name is fair game. Amiga Inc registered a trademark in Australia in 2006...
I would think that The only way to really clear it up is to track down everyone that could even possibly have any connection to Amiga, and have each of them "relicense" all Amiga copyrights with a BSD style license. Key would be to make sure that the copyrights they are licensing are worded broad enough to include anything and everything Amiga related. We don't have to worry about Patents, as those have all expired anyway.
I say BSD instead of GPL because all of the source might not even be available, and it would mean that they wouldn't have to break any up stream owners/licenses. Basically give the the out of "donating" whatever they may have, even if they don't know they have it. Once you have made it to the end of the chain, AmigaOS is free. Until then, you at least remove a bunch the elements in the debate over who owns it.