Yes, that's definitely the balance to maintain. Ease of entry, vs tooling to manage the project as it grows. The main reason I see it being an inhibition is due to the size of the HTML spec, and the number of pages that it will need.

I think this is why a lot of sites take markdown, then add their own extensions, like how there is "Github Markdown" among many other flavors. That's definitely one route, but I see something like ReStructuredText or Asciidoc as more mature and interoperable, while still being relatively easy to master in the same way as Markdown. Since they can both produce docbook output, vastly easing any migrations in the future by adhering to an industry standard.

It's not that easy. We have 60+k pages carried over from 15 years of organic evolution. It's unstructured and messy. A move away from HTML to something "more popular syntax" (like Markdown) is NOT easy.