As manager of several free software projects, I am familiar with feature requests that users of my project submit to its public issue queue.
Many of the suggestions are good, but having limited resources available, there is often no way I can assign a feature request to a member of our core development team. Core team members are on a salary, and in order to pay them, they have to do paid work (including working on feature-requests somebody will pay for having implemented). Our contract with paying clients makes sure that the result of this for-pay work always makes it way back into the free software distribution we make available for everyone, but there is little overlap between what paying clients request, and what is requested by members of the public. As a result there is always a huge backlog of feature requests coming from users that are not paying clients of our company and that are not willing to sponsor development. I.e. they want it for free. I've nothing against users that prefer to get their pet feature added for free instead of paying us to add it, I've just not yet found a sensible way to oblige.
We already have in place a pretty good system for managing and reviewing user's pull-requests, as well as a CLA that makes sure that user contributions can safely be merged into our project without creating future problems for our company or for downstream recipents of our software. We're just not getting as many as we would like of these pull-requests.
I first thought that we could provide additional support and some hand-holding to get the person requesting the feature to implement it. But after trying this out, we discovered that these users are not developers - they are literally just using our software. So the person requesting the feature is simply not capable of implementing the feature and submit a pull-request for review. To keep this question simple, just assume that all these feature requests comes from non-developers unwilling or unable to sponsor development.
So, given that the core development team can't provide this service without pay - how can I encourage users to implement features requested by other users.
What are the best practices when dealing with feature requests from the community, given that I want to minimize the cost of doing this for the company, while at the same time encouraging capable users to contribute pull-requests that implements (some of) the requested features?
To avoid this being closed as "too broad" or "opinion based", I am looking for specific strategies, backed up with references to real free software projects that has successfully encouraged and mobilized users to contribute in this way. The strategies can either be taken for relevant literature, or from personal experience.