Phabricator used to run on a similar system. You had to pay to send them bug reports & feature requests.

Sounds a bit weird for an open source project but I can tell you that the one company I worked at that used Phabricator did pay (and they definitely wouldn't have otherwise) so I think it's a viable strategy. Plus it makes you immune to slop!

On the other hand they did shut down a year or so ago though. Didn't say why.