Sometimes I feel like it HTML has been replaced when I view source on a JSON site.
That's a great point. In some ways, couldn't the basic structure of a web page just be a package.json file?
I think between JSON and Markdown, you wouldn't really need HTML. Interesting.
Aren't JSON and Markdown ways of defining content, as opposed to layout? You would still need HTML or some equivalent to turn them into a document, even if they are 'human readable' natively.
No. If you view source it will be a blank page. They use CSS for formatting.