That's sort of how it's currently set up. Gene makes changes to the TESTING version and releases it for beta testing. When it's been up and no issues have been reported (or issues have been fixed), he releases it to the stable branch. Sometimes Gene sends updates directly to the stable branch presumably because nothing significant changed and he is confident there won't be issues. If a problem occurs with the stable release, it's most likely related to a feature that wasn't actually tested in the beta branch due to available users for testing (the beta users didn't have the right hardware, etc to test the changes fully). Either that or the update has a bug that doesn't show up for some time or is harder to track down (e.g., slow memory leak).
It sounds like you are proposing some way of rating the released version for stability after the fact. That sounds like a good idea, but I'm not sure how that would be implemented. I don't know if people with a stable version would come here to rate an older version.
Perhaps this could be a feature added into HG where after some number of days/weeks HG pops up a dialog to rate the current version. I don't like popups, so I'd recommend that if something like that were implemented, it should have a way to disable it in settings. Perhaps at that same location there should be a way to rate it instantly as well.