> 1. Making it possible to do something like <template src="..."> and being able to load them from an external source

I've done that, requires no build step/npm/whatever. It was posted on HN for discussion a week ago: https://github.com/lelanthran/ZjsComponent

As a web dev you probably already know but #1 is slightly similar to `Web Components` but you're right we cannot load a web component right in the HTML where we use it. It makes sense though because if you use an Element in multiple places it wouldn't make sense to have 'src' in multiple places, so ultimately some kind of 'loading' at the top of the page is needed, and that's how WebComponents work, but I still like how you think.

#3 is a tricky one syntactically because HTML needs to be used by mere mortals and JS is a programming language used by us gods, so unifying all three would br tricky, but again I agree with you that would be awesome. Maybe some flavor of LISP would be both "powerful like a language" and "easy like a document".