Between that, HTTP2/3 and ES modules many of the downsides for building apps with no compile step are almost completely mitigated.
IMO build step woes are really overstated, my build step has linting, type checking, optimization, bundle analysis size diff checks, enables JSX, and is basically necessary for development anyway as you get hot reloading, compiler-added features for better debugging, etc.
I haven't done js since jquery days, but keen to get into modern js development
It used to, but browsers ruined it because they didn't want to help improve caching support
If you don't have tons of code, tree shaking and minification is not that important. If you depend on a couple libraries (Jquery, for example) those can be minified and just refered to directly in the source.
As I remember, it never saw broad adoption because it was technically challenging to integrate with, and it tended to push a lot of resources clients already had, so it wasn't a big win for efficiency anyway.
They use slightly different wording but are describing the same basic idea: This syntax will be ignored entirely and then optional/other process can use this area for whatever.