I haven’t yet have time to process and curate the list, but I have some OSS candidates for bounty systems here: https://codeberg.org/teaserbot-labs/delightful-funding/issues/1
Liking this ideas. It has its merits and challenges as you say, but can be a great way to get an involved community, and also you can measure interest for certain features by the pledges that are coming to them.