Elixir is already one of the most static of dynamic langages so I'm not too surprised about the quick progress, the language is almost built for that already.
It's much easier compared to typing Ruby or JavaScript in terms of difficulty.
Exactly! The hard part was to find a type system that we can map most (if not all) Elixir constructs to, and set-theoretic types have been a great fit so far and we were able to develop the theory in the areas where it lacked.