The current W3C status of the CSS Selectors Level 4 is a Working Draft which was last updated on .
If you want to take a look into the latest working draft by the W3C you could do that on the Selectors Level 4 document.
The latest, regularly updated and somewhat unstable Editor's Draft document could be found as the W3C editor's draft.
So far the World Wide Web Consortium is working on the specification which is not finalized, so there is currently no release date available.
Please note that there is no solely CSS4 on that note, any mentioning on our site refers to the Selectors Level 4.