In case you glossed over it, I think he said it in his post:
"But down the road, I may want to build a page that contains an interactive visualization, a filterable table, or a demo of a React component I'm open-sourcing."
Here's an example of embedding a WASM home computer emulator with just a few lines JS (and I'm not exactly a web development expert, so with a bit more knowledge and experimentation I'm sure this could be made much more fancy):
I'd like the ability to embed arbitrary React+JSX into my Markdown, something which can theoretically be done (i.e. with the Hugo Babel plugin). But then I immediately realized I would have issues with importing my styling libraries (I used a custom-built Tailwind-esque set of emotion[0] classes) and using React Hooks.
As you can probably tell I have a hard time letting go of the power/flexibility of the React/SPA approach since it's all I've used for several years now.
Haven't yet seen a reason to switch to anything else.
SVN rocked because you could run static sites in it, a little bit of jquery and whatever and I was building a ton of simple business productivity tool as single page apps. All with the peralta guarantee of support.
With Hugo/Zola I set my generator to include MathJax javascript if I enabled it in the front matter of the post. Etc.