I would like to know when Chrome's declarative web request API will be in the stable channel (https://developer.chrome.com/extensions/declarativeWebRequest). I realize that is asking a lot. I'd like to write an extension that depends on a beta API though and am just curious if there is a best approach for guessing when it might become stable.
declarativeWebRequest is not currently scheduled for promotion to stable. There were some issues with certain use cases that made the current design and implementation insufficient for the long-term support that stable would entail. We have not announced plans to proceed further with the API. You can star http://crbug.com/112155 for updates.