I wonder if he actually tried embedding HTML into Markdown, because that's as simple and straightforward as it can be: just start writing HTML in the Markdown document, and after the closing element, continue with the markdown text. This should completely cover the requirement to embed interactive elements into markdown using a static site generator like Hugo or Jekyll without having to deal with an overly complex dependency like React.

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):

https://floooh.github.io/2019/01/05/wasm-embedding.html