I don’t think there is a way end users can sponsor enhancements using a bounty system, many can’t afford engineering time but would be happy to throw in $10, $100, $500 towards getting a fix or feature. I have used them before for other projects, its actually quite exciting when you get a feature you were part of requesting, it’s not gambling. 
Currently users interest may come to an end, they may get a sad face instead.
Maybe maintain a visible list of top 10 things based on what’s asked for a lot, then user can vote, have ability to donate, have ability to start a new one for a fee.
Links to a bounty could be maintained in places where people end up finding similar requests like Collabora bugzilla Issues, Collabora forum, perhaps TDF LibO-MSO comparison
Is there an open discussion anywhere about the pros and cons?