I wrote a plan on releases a really long time ago here: Discussion: release cycle
But the primary reason it’s not easy to implement any kind of “filtered” release seems to be the difficulty of removing a pull request/feature that was already merged.
Due to this our flow now is strictly “once everything in master is ready then we can upgrade it to next stage”. Which of course creeps on forever.
I think Kenneth has been hesitant to push any more releases exactly because of that overhead and uncertainty about the quality of recent changes.
On the flipside i try to make sure all pull requests have feedback or is merged within a short time to avoid discouraging contributors. A short turnaround time between opening the PR and seeing it in canary is in my mind the only way to keep people involved in the process.