I'm not sure I've seen any "user interface innovation" done with HTML.

Pick a book on GUI interfaces of the 80ies (for example: Computers Graphics by Foley & al), and see that pretty much all UI paradigms themselves were pretty much explored back then. The concept of the "hypercard" was already there.

HTML just improved on the presentation of it, often worsening everything else. Somehow web apps lowered the expectations of what a computer /should/ do so much that usability itself became an afterthought.

Some of the best designed apps on the web mostly ditch the DOM and layout everything in JS. Hardly "innovative".