My experience is that often even when the user comes with a suggestion backed up with a patch, it can be rejected because either they didn't understand how it interacts with other features in the codebase, or the maintenance burden would be too high for too little gain.

Essentially even when you're asking to contribute a patch, you're requesting that someone maintain some code you wrote for an indefinite span of time.

My experience has been that it's much more productive to say "I can't merge that patch into the core, but here is how it would be implemented as a plugin" and ensure your plugin interface is powerful and stable enough to allow people to do what they want.