Last time I heard something like this discussed, one of the suggestions was "browsers automatically disable support for experimental features on Tuesdays", which should allow people time to experiment but should prevent them from depending on it in production. Also, it's a simple rule that can be shared through the web development community by word-of-mouth[1], and many browser vendors can share it without having to coordinate infrastructure, etc.
[1]: Obviously this wouldn't be the only way to share it, but when one developer can turn to another and say 'why doesn't this work' and get a one-sentence answer that contains an accurate model for predicting future occurrences, it's a lot more likely for that model to be reliably propagated via Stack Overflow, Twitter, the random mailing-lists-reformatted-as-web-forums content farms that crop up in search results, etc.