It's not clear that Fable would fit the constraints, especially since F# heavily relies on reference types for discriminated unions and lots of other features. It's possible that Fable wouldn't be able to compile down to lower end embedded platforms, or even things like Linux eBPF applications (like my transpiler can do).

You can for some features tag the type with a [<Struct>] attribute and it will compile down to a struct/value type representation. That includes records, DUs, active patterns, etc.