Babel has a lot of plugins, and hopefully people don't have to learn all of them. How many people use stage-0 plugins for bind operator or do expressions?

You're right that Babel (and TypeScript!) implement features earlier than they land in the spec, but at least TS does so only when it's almost for sure going to make it in (around stage 3) and people probably shouldn't be using stage 0-2 plugins for anything but experiments, IMO.