That's readable in the simple case, (arg1 is a string, returns a string). What about the more complex cases? Different method signatures, required extra arguments, returning objects or arrays? This will either a) break in those cases, or b) not be applicable. In which case, it's extra complexity for very little gain.

Seriously, this just seems like syntax sugar that just isn't needed. I get that you might not think it's elegant, but is anyone seriously troubled or confused by method3(method2(method1(str)))? How would the pipeline syntax help here?

Yep; same reason Lodash implements _.flow and _.compose.

It also encourages you to write methods that take a single argument and return a single value, or partially apply those that don't.

It's much less clear than the F# and Elixir versions of |> are, so if you've used those languages this feels confusing looking. It would be nice to introduce |> into Javascript while keeping it just as understandable as it is in every other language that already has it.