As for bounties, I think it messes up with the OSS governance model. Let's say there's a bounty for feature X. You implement the feature, want to merge it in, but the maintainers don't like it and don't want to merge it. Now what?
Yeah. Science has a (some would argue) slightly more sophisticated approach to bounties in the form of grants. The inconvenient part is that many things ending in "Foundation" in open source have no resemblance to things like the NSF.