XHTML failed in an era when writers (even normies) were writing some HTML of their own and they could't be trusted to close their tags properly. XHTML also assumed writers would be personally invested in semantic markup like distinguishing e.g. the italics of book titles from the italics of emphasis.

Today, when writers are using visual editors (or Markdown), few are writing their own HTML any more. A web standard requiring compliance would work differently today.

Markdown sux and so do visual editors. I think visual editors were just invented to make it so cut-and-paste never quite works right. There's been some conceptual problem with the whole idea ever since MS Word and the industry has never dealt with it.

> XHTML failed in an era when writers (even normies) were writing some HTML of their own

I'd say it was a minority of writers that were handcrafting XHTML. And it was the case that everyone or their handcrafting or using tools could validate their compliance using a browser which made it very easy to adjust your tools or your handcrafted code. We are now in a situation where there is no schema for HTML.

I, for one, am very much in favor of forking the web with a document format with a schema. It really seems like a small and simple change to me.