The Let's Encrypt initiative, which exited beta back in April, is doing some of that work by providing sites with free digital certificates to help accelerate the switch to HTTPS. According to [co-founder Josh] Aas, Let's Encrypt added more than a million new active certificates in the past week -- which is also a significant step up. In the initiative's first six months (when still in beta) it only issued around 1.7 million certificates in all.
The "50% HTTPS" figure is just a one-day snapshot, and it's from "only a subset of Firefox users who are running Mozilla's telemetry browser...not default switched on for most Firefox users (only for users of pre-release Firefox builds)." But the biggest caveat is it's only counting Firefox users, which in July represented just 7.7% of web surfers (according to Statista), behind both Chrome (49.5%) and Safari (13.68%) -- but also ahead of Internet Explorer (5.4%) and Opera (5.99%).