They should have stuck with the F# proposal. The hack proposal just takes one more giant step toward turning JS into Perl.

Hack proposal

    value |> foo(%) for unary function calls,
    value |> foo(1, %) for n-ary function calls,
    value |> %.foo() for method calls,
    value |> % + 1 for arithmetic,
    value |> [%, 0] for array literals,
    value |> {foo: %} for object literals,
    value |> `${%}` for template literals,
    value |> new Foo(%) for constructing objects,
    value |> await % for awaiting promises,
    value |> (yield %) for yielding generator values,
    value |> import(%) for calling function-like keywords,

F# proposal

    value |> x=> x.foo() for method calls,
    value |> x=> x + 1 for arithmetic,
    value |> x=> [x, 0] for array literals,
    value |> x=> ({foo: x}) for object literals,
    value |> x=> `${x}` for template literals,
    value |> x=> new Foo(x) for constructing objects,
    value |> x=> import(x) for calling function-like keywords,

F# proposal would make `await` and `yield` into special syntax cases or not allowed.

I'd rather do await/yield the old fashioned way (or slightly complicate the already complex JS syntax rules) than add the weird extra syntax. Arrow functions are elegant and already well-known and well-understood.