I was referring to chenglou's comment[1] where he said "It also prevents some optimizations and new type features."
I think what @chenglou was referring to are issues like the "value restriction" [1] and the need to wrap "uncurried" FFI functions with a function that "adapts" it to curried form, thereby adding a layer of indirection.
Reason does not solve these, they're problems inherent to the underlying language and the choices made. I think the point being made was just that currying isn't a clear step forward, but causes some problems as well.
Yeah, definitely agree that there are trade-offs with currying when mapping it to a compilation target like JS, and I am consistently impressed by Bucklescipt's ability to convert the curried versions of functions to regular JS calls. That said, I do still think that it's worth the trouble!
Not sure what optimisation problem you're referring to, Reason and OCaml underlying AST are exactly the same. There are no actual tuples unless the programmer is creating actual tuples.