I'd say the problem isn't "this is not JSX", but that the syntax just looks awful:

     div []
        [ div [] [ button [ onClick Increment ] [ text "+" ] ]
        , div [] [ text <| toString model.counter ]
        , div [] [ button [ onClick Decrement ] [ text "-" ] ]
        ]

JSX isn't the only syntax that took off, there are for example indentation based syntaxes for HTML, theoretically:

    div
      div
        button onClick: Increment
          text "+"
      div
        text <| toString model.counter
      div
        button onClick: Decrement
          text "-"

already much nicer (and if it was all wrapped in parens it wouldn't make much of a difference).

Given that Elm is "just" for making HTML apps, this does seem like something the language should focus on.

Your syntax only looks good in hello-world examples and will stumble upon the same sort of ambiguities that things like coffeescript grappled with.

It turns out that it's less work to always have delimiters than it will be to have to add them anyways to disambiguate.

It's an interesting balancing act. I think when most devs look at JSX for the first time they instantly recoil at the rebellion against years and years of "separation of concerns", yet as you say it's a syntax that devs have embraced regardless.

I love Elm and think it or something very close to it should become way more mainstream, but I do find its bracket-heavy DOM syntax off-putting in comparison.

EDIT: That said, I do agree with the leading commas in laying out models as opposed to the trailing. Scanning the models of an Elm file is far faster than, say, a JS file, subjectively at least.

HTML and XML for describing documents also never took off; they are largely generated from something else rather than hand-edited.

Thus, no structural, recursive syntax for document editing has "taken off".

Word processing is still done in Microsoft Word by most of the planet. HTML e-mails are written in some WYSIWYG client program. Web forums use variations on markdown (with raw HTML only as an escape hatch).

People do work with *ML by hand, but largely reluctantly.

If you do have to roll up your sleeves and work with the serialized syntax, you're far better off it its is S-expresions.