It was a pleasant surprise to see @reisenberg 's post in discuss.ocaml.org ! I feel happy that a prominent Haskell compiler contributor has joined us 
. Welcome to the OCaml community !
Thanks for giving an insight into what the Jane Street compilers team is working on for its customised version of the OCaml compiler. I would naturally expect Jane Street to use more and more of these custom features in its own codebase going forward.
But because of the way development generally works many of these custom features may never find their way into the main OCaml trunk (e.g. wider OCaml team disagrees on the inclusion of the feature for any number of reasons) while some of them might arrive after a significant delay. The delay is likely to be significant on the order of ~years as consensus is built and implementations possibly modified/peer reviewed in the interim.
While the intention and desire may be to always upstream the reality is that there might be an increasing divergence in the compiler codebases.
In the meanwhile the OCaml community depends a lot upon Jane Street libraries. How would the newer versions of the libraries that progressively use more and more of custom language be made available to the OCaml community?
I would suppose you would need to strip out all the custom features so that it can run on plain vanilla OCaml or use something like cppo ? Will that always be practical though?
TL;DR How will this enhanced push towards using a custom OCaml compiler impact Jane Street’s future releases of open source OCaml libraries that currently only need a vanilla OCaml distribution?
Slightly Offtopic
I asked @snowleopard (another notable Haskeller who joined the OCaml community) a year ago:
It would be interesting to get your experience on the transition into OCaml. What do you find good/delightful in OCaml generally speaking (and in comparison with Haskell) and what would you like to change in OCaml?
What followed was an interesting response – See [Job] Build System Engineer at Jane Street - #3 by snowleopard
It would be great to get your insights too, Richard Eisenberg, should you feel so inclined to answer !