All that can be done without semantics. But HTML is also a document-oriented semantic language. Your way would just have idiosyncratic elements, which is little different than a div from the perspective of the rest of the world.
Until then, a custom element is just a div. Semantically opaque.
When we have actual consensus on elements and semantics, that enables very rich clients that can provide an alternative view over the same information, regardless of prior styling. For example, imagine if hovering over any time element will also show you a visual ticking clock or calendar. We wouldn't be able to do that if we didn't have consensus on the semantic meaning of time as something more than a valid token for a parser.