I'm actually surprised that you ask at all. I've always seen the backing process as a way to enable the production of the game and the documentary, not as a way to buy an exclusive copy of it. It's your content, do with it whatever you want. If you decide to open source the complete game at some point in the future, just as id Software did with Doom, I would be fine with that, too. Actually I would love to see you doing it. The documentary deserves to be seen in public. Do the history of game making a favour and upload a copy of the documentary to the Internet Archive so that it gets preserved for future generations.