To descriptively move the needle on the semantics of custom elements you must first move the world. Any semantics you attach to your custom elements really is just your semantics. If you want this to change then start persuading everyone that your custom elements ought be semantically observed.

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.