This is a really exciting idea to me, but this website is pretty anemic (guessing it's a work in progress?). Kinda surprising to me, given the 7K stars on github. Maybe it should be submitted when it's a little more filled in?
Personally, considering how ambitious the project is, I was hoping they would go just a bit more ambitious and cover type checking as well (rather than just transpile out the syntax), otherwise we still need to install Typescript/flow and run their parsers independently from rome.