Being able to properly type data structures is the most interesting part of types for me. It’s all I ever missed in Ruby (and used Virtus/DryStruct). This comment mentions casting which would be interesting. It would be cool to have something like changesets in the standard lib that works across data types. I don’t know if that’s a big ask or a terrible idea or anything, just saying it would be cool 
Do libraries like HTTPoison not validate their options? I’ve noticed some libraries do which I always appreciate and never really thought about if there are ones that don’t (I haven’t had to deal with much production config in my time writing Elixir).
