[baweaver]

The intention right now is for the StdLib to provide known types to build off of written in RBS. There's no requirement to use them necessarily.

Steep and Sorbet are second-level, they build off of RBS. Matz has mentioned offhandedly in conversations I'd had with him in the past that there's a ton more in store with RBS beyond just type checking, so we'll see where they go with it.

As far as YARDoc I've been eyeing that one for a while now since I first heard about Steep at a Braintree Ruby meetup before Soutaro was at Square. We're still talking about what and how as far as that one.