generic vs closed platforms

Actually I have to admit that despite my own "hand-waving" talk above, I haven't quite given up on the idea of people getting together to offer software bounties, if the right conditions can be had. I'm actively considering trying to set up a portal for that, based on the idea that the task set should be based around a bug ticket on a project's bug tracker (so that project developers can review it and have their say/give their advice before people start putting in money, and can guide the person doing the work) and that the bounty is a bonus to the person doing the work, but almost certainly not their main motivation (perhaps they are also affected by a bug, or want to get to know a project's codebase better or to gain new experience...)