> Is there any place in the official OCaml repository / issue tracking system / wiki etc where one could check the status?

You can see some things on:

  https://github.com/ocamllabs/ocaml-modular-implicits

but you shouldn't take a lack of activity on there as a sign nothing is happening. For instance, Frederic is actively hacking on the prototype at the moment but hasn't pushed anything to that repo.