1ML just shows that advanced (first-class) ML modules are really just System F_omega. That's just barely more than Haskell! More languages need to expose it nicely. But we already have most if not all the technology we need to make them efficient and worthwhile, vs just possible. This isn't a research problem. This is a design/HCI problem.
ML modules are great, but I'm not convinced that making them first-class (1ML) will be equally great. ML hits a sweet spot between automation (full type inference) and expressiveness that is only possible because the type language is first-order. This is IMO the point that most extensions on top of Hindley-Milner completely miss.
So, if anything, what I'd like to see is a dependently typed language whose type language is a first-order, computation-free (no non-constructor function application) subset of the value language.
The 1ML papers discuss this, ML implementations in reality are already incomplete with regard to Hindley-Milner, a quote:
"We show how Damas/Milner-style type inference can be integrated into such a language; it is incomplete, but only in ways that are already present in existing ML implementations."
