No-one could even agree on making HTML5 valid XML - in order to leverage all the tools and knowledge that exist in that space.
Not that I even like XML. But having another XML dialect that's not actual XML shows that the only hope is to build valid tools and abstractions on top of all the crud.
There's nothing "not actual XMLish" about HTML. HTML is formally describable in its entirety using SGML (see my project at http://sgmljs.net/blog/blog1701.html), just not by the XML fragment of SGML.
You're missing the point. HTML wasn't XML because XML didn't exist then. SGML did. XML is a "an SGML dialect that's not actual SGML," not the other way around. The people who designed XML knew the SGML spec, as they wrote XML as a subset of it, and they knew what was in HTML. They could have written XML so that HTML conformed. They chose not to. But the HTML spec at the time was absolutely conformant SGML.
What cwyers said. Plus, XML was designed to replace HTML as XHTML, but it didn't happen. Doesn't mean you need to give up markup processing alltogether. Just use full SGML, which has additional features such as tag omission/inference and other markup minimization features for text authoring not in the XML profile of full SGML such as markdown and custom Wiki syntax support. You might actually like it.
You can parse HTML 5 into XML using my HTML 5 DTD [1] and eg. OpenSP's osx tool or my upcoming sgmljs.net tool.
What do you have against DTDs? They do the same as XSD, and then some.
Not that I even like XML. But having another XML dialect that's not actual XML shows that the only hope is to build valid tools and abstractions on top of all the crud.