There's still so much out there that could be improved on HTML documents.
For example the HTML -> Print pipeline is mess. There's all different types of messy tooling to convert HTML a PDF and then to Print. We should be able to have tex-like reproducible styling for our HTML documents.
(or for that matter e-readers! We should've never needed to create new formats for displaying text on an e-reader. HTML should've been more than capable!)