It isn't that this new syntax is slow, so much as V8 has a shit-ton of internal machinery dedicated to optimizing specific execution paths, and it is those thin

It isn't that this new syntax is slow, so much as V8 has a shit-ton of internal machinery dedicated to optimizing specific execution paths, and it is those things which get a massive efficiency boost. In that sense, becoming syntax complete is just a first step down a very long road.