The real downside to this, of course, is auto-playing embedded HTML5 advertisements replacing Flash based ones. More secure yes, but far less easily blocked by browsers without extensions. Another problem is that HTML5 video, like you find on news sites, are also set to autoplay and cannot be blocked, as they do not depend on a plugin or extension, without blocking that domain from loading with NoScript or similar. This wouldn't be a major problem except in the USA, a country with the worst internet in the developed world, unlimited internet is simply not an option for tens of millions of people (not counting the "unlimited" which are just "unlimited until you use XX, then you get reduced speeds), and those megabytes add up...
And I speak as one of those people who, at home, get 20GB per month, 666MB of data per day, before speeds are reduced to 1mbps, and in 2019 terms, that's slower than 56k.
