Seldom mentioned in type system discussions like this is the notion of openness. For instance, F# is one of the very few languages addressing openness where sch

Seldom mentioned in type system discussions like this is the notion of openness. For instance, F# is one of the very few languages addressing openness where schematic structure in data can be directly and type-safely reflected by the type system e.g., using "type providers." This general area of research is relatively untapped and, in my view, offers huge potential given weak links with conventional type system/data bridging solutions (eg code generation). Structural types emitted from something like type providers would be a game changer.