I think a major issue with this approach is just practicability - I'd want to write my content in something like markdown and we will anyway need JS to convert the markdown to HTML.
I have also been interested in making SPAs, my my way is more traditional. Using javascript for the stitching. But only Vanillajs. I don't use any frameworks and bundlers for my SPAs. In fact right now I am working on a simple blog: http://rishav-sharan.com using just HTML, Vanilla js and Tailwindcss.
If anyone is interested in my approach, I have an article detailing things there, or you can just read through the source. Its un-minified and fairly readable.