Oleg just posted a new page, First-class modules: hidden power and tantalizing promises, related to new features in OCaml 3.12 (on LtU).
First-class modules introduced in OCaml 3.12 make type constructors first-class, permitting type constructor abstraction and polymorphism. It becomes possible to manipulate and quantify over types of higher kind. We demonstrate that as a consequence, full-scale, efficient generalized algebraic data types (GADTs) become expressible in OCaml 3.12 as it is, without any further extensions. Value-independent generic programming along the lines of Haskell's popular ``Generics for the masses'' become possible in OCaml for the first time. We discuss extensions such as a better implementation of polymorphic equality on modules, which can give us intensional type analysis (aka, type-case), permitting generic programming frameworks like SYB.
It includes a nice intro to first-class modules by Frisch and Garrigue: First-class modules and composable signatures in Objective Caml 3.12.
OCaml definitely just got even more interesting.