It's worth mentioning that Pyret followed this path. It was originally a Racket #lang. Once we got the design off the ground and decided to primarily target the browser, we wrote a new implementation in JavaScript and Pyret. The tools in Racket (including ragg [http://docs.racket-lang.org/ragg/]) were invaluable in getting started quickly.

This archives the state of the system when we made the switch:

https://github.com/brownplt/pyret-lang/releases/tag/pyret-20...

Some things, like the grammar (https://github.com/brownplt/pyret-lang/blob/5f22ec7c8affde15...) have survived largely intact from that prototype for years.