It would be great if movie companies at a certain point where the commercial value, present or foreseeable future potential, has become pretty low, just say to hell with it and let it go. Outside organizations, the communities etc., could raise their own funding so it could be done without costing the movie company almost anything. They could charge those organizations on an at cost basis (or a little profit if necessary) for the use of equipment and facilities and such, while they digitize as much as they want (all, whatever) and just release it for free.
The best way to preserve this stuff is to just release it to the public, as you say, all of it. It will get passed around online and there will be so many copies out there it creates massive redundancy that no one organization could ever match.
I sorta went off topic there

, due to Fury Road this stuff certainly does have commercial value now, but still I also agree with the just release it all for sale idea too. And don't be terrified some fan will put together something with it that might potentially affect sales of some future thing that you'll never do anyway

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