At my last job, we did something similar to what iOS 9 is now doing, where we migrated a survey engine to serve all forms over https. There was high fiving and champagne all around the engineers desks, while media was freaking out that their impressions took the sharpest reverse-hockey-stick in the world. Ad networks are seriously the worst when it comes to https traffic. Given the dozens of redirects and pixel injections and iframes slapped into a media page, it's nearly impossible to serve secure traffic since it only takes one network to downgrade the https request to http and then the page is "broken".