Is the scry mulligan rule implemented in the rules at large yet?
The new mulligan rule was officially added starting with Battle for Zendikar prereleases on September 26-27, 2015 (or October 9-12, 2015 for Magic Online).



As of this question being asked, it was definitely not a rule yet. In fact the Latest Developments column on August 7 said:


  We will be looking at both how the Pro Tour played out, as well as the reactions from the players regarding the rule. I don't know when we will have a decision based on this, but we hope to have new information fairly soon.


Anything official will surely be on the official site, so I wouldn't bother digging on forums or anything - things like this happen in official ways, not just via rumors and forums.