Yours kind of does but I am not a fan of the dot syntax. Though I don’t see other possibilities. Might indeed be something that confuses LSP, no idea, haven’t tried. It just feels off; it’s forced on a language and runtime that are not made for it.
It’s not too different at all, it’s just about making people use something else which turns out to be super difficult with Elixir. A lot of people are already comfortable doing things certain way. I would give it an honest go however, once or twice.
Structs + strict validations. When you are NOT on the edge of your system it then becomes a simple matter of just pattern-matching on a struct because all the functions that produce them (i.e. after parsing complex JSON trees) ensure many properties. Works pretty well. Though I do agree the lack of sum types in Elixir is sticking like a sore thumb. 
I don’t think they are rivals, I’d attempt to use both. But have to admit, I’d default to Ecto.Enum first.
Your idea is great and as a Rust fan I really really want sum types in Elixir. But I just don’t see how would that even work with the current realities of the BEAM VM. As much as I like the idea I’d lean to enforce stricter and more exhaustive pattern-matching clauses comprised of tagged tuples.
