I don't know much about web components, but they seem like a good fit. Though I would be pre-processing them into regular html. Though the more I think about it, having markdown is nice for a number of reasons, who knows maybe I'll come up with some insane hybrid.
If (but lets be real, more like when) I make a custom SSG for my website, I can see it being based on HTML rather than markdown. I pretty much just use Hugo for partials and shortcodes now, I populate all my pages with feeds manually.