OK, but if we're going to have .rbs, why not just modify the ruby syntax to allow .rbs-style types inline? Especially becuase .rbs already looks like class and method definitions without the bodies. So... just add the bodies.

    class Merchant
      attr_reader token: String
      attr_reader name: String
      attr_reader employees: Array[Employee]

      def initialize(token: String, name: String) -> void
         # actual method body
      end

      def each_employee: () { (Employee) -> void } -> void
                   | () -> Enumerator[Employee, void]
          # actual implementation body
      end
    end

It seems like they are trying to support existing competing work... but i'm not sure any ruby users actually want that. I prefer this .rbs to sorbet all around, and would prefer it inline.