First of all, with the actual proposal, wouldnt it actually be like this? with the %.

    xs
      |> map(%, x => x * 2)
      |> filter(%, x => x > 4)
      |> sorted(%)
      |> take(%, 5);

Anything that can currently just chain functions seems like a terrible example because this is perfectly fine:

    xs.map(x => x * 2)
        .filter(x => x > 4)
        .sorted()
        .take(5)

Not just fine but much better. No new operators required and less verbose. Just strictly better. This ignores the fact that sorted and take are not actually array methods, but there are equivalent.

But besides that, I think the better steelman would use methods that dont already exist on the prototype. You can still make it work by adding it to the prototype but... meh. Not that I even liket he proposal in that case.