I need release date (month) for stable version for SQL Developer 4.0?
well, it seems you are new to the world of oracle release manners...
You will definitely not get any information regarding your request.
Just sit and wait and be happy when it's there someday.
Don't worry. You are not alone :-)
We'll have at least another Early Adopter release and fix bugs until it's 'ready.' You won't have to wait that long for the official release, but as Andre said, it's not our policy to publish dates. And even if we did, we'd most likely be wrong.