Hi, Bert. The new Disqus was designed to address issues we saw with the older version where conflicting CSS or custom code in the theme editing tools would often conflict with a certain page element, break certain features and/or confuse users. So the new version uses an iframe approach, partly to address these issues and UX consistency reasons, but to capture a number of benefits having to do with security, SEO and performance.

The research we did showed that admins wanted look and feel continuity but wanted to do less work to achieve it, so we instead designed the adaptive iframe to auto-inherit components of the page, e.g. dark vs. light palettes, link colors, fonts, etc. The HTML5 design also tends to render a lot better on mobile and tablet than the older, stripped down mobile theme, and is more or less at feature parity with the desktop experience (another thing we heard that users have come to expect these days).

(tbc...)