The namespacing is indeed ugly. HTML's current tag soup might be legacy filled, but we haven't replaced it because it's convenient to have short memorable tags

The namespacing is indeed ugly. HTML's current tag soup might be legacy filled, but we haven't replaced it because it's convenient to have short memorable tags for these things. XML namespaces failed in this, never letting you mix two namespaces on an equal footing. If HTML is to go beyond just HTML, then we're going to see much more variety in web content and markup. In that case, doesn't it make more sense to stop worrying about a universal, global tag standard, and instead see it as a 'from module import x' type of problem instead? Let the document author figure out how to map tags in, and make it as easy to import a vanilla HTML baseline as HTML-with-a-dozen-bells-and-whistles.