Let's say you settle on a 2-4 weeks timeframe to take the RC through rough waters and encourage people on the forum to test as much as they can and let it do some heavy lifting internally as well.
It's not that there was no feedback about problems with the 1.2 dailies and RCs ;) There were, in fact, issues and I think it's clear that the new displacement for example failed on simple tests for some people.
I totally understand how hard it is to track down bugs or even come across unusual bugs, more so if those who run into problems are not able to supply any scenes. Still, releasing a final version means that people will take the 'final' tag as s sign of a stable and tested release. With this in mind, 2 days of testing of RCs is not enough, no matter what.
Make a subforum for each RC. Supply scenes that people can test on their machines (even if simple or exotic), encourage people to upload their own scenes for testing for others, let them discuss new features (the new sun was an unwelcome surprise for many users, for example) and get some feedback. But, please, take the time to make sure it's stable and a broad range of users had the chance to test it. Once a final release is marked as unstable by the user base, no one will want to run it in production.