Thanks @LostKobrakai, great insights and the EEP-0069 link was a good read.
I guess the closest type I can express the string maps would be:
%{required(String.t()) => term()}
Considering the limitations you mentioned, which would require some big effort to support it.
I think with the new type system for Elixir (which will not use Erlang’s types AFAIK), may introduce ways to express better the type for string maps 
, but that’s only a guess.
