Hey bcherny! Yes, dog-fooding (self-hosting) has definitely been a huge part in making TypeScript's development experience as good as it is. The upside is the breadth of tests and infrastructure we've already put together to watch out for regressions. Still, to supplement this I think we will definitely be leaning a lot on developer feedback and will need to write more TypeScript that may not be in a compiler or language service codebase. :D