(X)HTML5 needs to be modularized like CSS. I can't remember how many times I've clicked to view something in the (X)HTML5 spec and had a hundred megabyte webpage load. It's nice that they are no longer shooting for I think it was a 2021 release or something wild like that?
What is most important is that long standing bugs in the browsers be resolved along with specific standards being given special emphasis.
I only support IE8 officially in regards to CSS2 and only barely test IE7. With Microsoft's cards of politics on the table either the browser supports native feature without a problem or I lock it out intentionally, tell users to change their browser and don't support it unless someone wants to pay me dearly for the trouble. IE's market share last month was 11.8%, people need to figure out how to do statistics right and start using object detection.