I don't know, but you raise some really interesting points, and we didn't even talk about the quality of the documentation that might be produced. Bounties might be the wrong way to do it, but I can imagine a Patreon-style approach might work. Like "I'm the developer on this, and I'd rather be writing code. But if people contribute $X to my Patreon I will dedicate 5 hours a month to working on the documentation, instead".