Sorry, but HTML isn't going anywhere. XML had its chance — full support from W3C and implementations in all-but-one browsers for a decade now. text/html parsers survived that.
I don't think you can convince all browser vendors to bet on XML again. They all opposed XHTML2. W3C tried to push XHTML2 without them and ended up making HTML even stronger.
XML with vector shapes? We've got SVG. It may not be perfect, but has tools and implementations.
Easier CSS layouts? Flex box, grids and calc() are around the corner. They'll be usable sooner than HSS, and kill the project by being good enough.