well, just two cents from an old man: I understand the wish for having everything under a public license but this is NOT the major issue here. As I wrote elsewhere: We have the sourcecode of the game itself and basically ALL maps. I have no doubt that Red, Pardner and Joe Kari would release their maps if required. We have the sources for those anyway so they are not lost. We also have all ICI canon map sources.
I also don't think that anyone would be able to make a case against us because of the player models. Thats quite far fetched IMHO but I am no lawyer.
The only assets that really need clarification are textures, sounds and maybe models if anyone used 3rd party models at all. But that can be handled. Just throw out the old textures and create a new texture repository e.g. by using textures.com. Thats what I used for Sweetwater at least. License wise that is fine IMHO.
The real issue is that a team (!) needs to pick this up now so that the game gets an infusion of fresh blood, new ideas and (wo)manpower ... content licensing issues can be sorted out. Lack of manpower cannot.
On the bright side: It was always like this!