Static types without performance benefits. So far, all popular static type systems have had the performance benefits, so it's unclear how much people value the other benefits (quality and documentation).

I wonder which will have the most impact: code quality or types as documentation (esp for tooling)?

They are adapting to common idioms, rather than designing it from the ground up. This ad hoc approach is a great way to build useful tools (and startups), but it's also usually a mess. Like NN4. But, they seem to be type experts - plus they're using ocaml. Maybe ad hoc by experts is the way to get these ideas adopted?