>Your language should be designed such that the cutoff is up to you, the writer of the code, and really just a matter of syntax, not semantics.

I have more important things to think about in my code than when I switch between two dialects of the language.

Especially since I get no extra expressive power by doing so.

>Obviously, I (usually) would not want to write things like

Or just use (+ (* a b) (* c d)) which is simpler that any of the example above. Then I can chose between any of:

    ( +
      (* a b)
      (* c d))

    ( +
      ( *
       a
       b
      )
      ( *
        c
        d
      ) 
    )
    

Or whatever else you want to do.

>As the border between these can be fluid, where you choose the cutoff will depend on the situation and also be fluid.

It's only fluid because you've had XX years of infix notation caused brain damage to make you think that.