Do you mean Ruby lacks syntactic support for adding type annotations inline in your programs?

I am one of the authors of RDL (https://github.com/tupl-tufts/rdl) a research project that looked at type systems for Ruby before it became mainstream. We went for strings that looked nice, but were parsed into a type signature. Sorbet, on the other hand, uses Ruby values in a DSL to define types. We were of the impression that many of our core ideas were absorbed by other projects and Sorbet and RBS has pretty much mainstream. What is missing to get usable gradual types in Ruby?