There's a screencast fresh off the presses on the info page at https://ocaml.io/w/Blog:News/A_new_Reason_for_OCaml

I'm finally going to switch away from my ancient nvi setup and use Atom instead! MirageOS recently moved all our libraries over to using the new PPX extension point mechanism in OCaml instead of the Camlp4 extensible grammar. This means that MirageOS libraries should be compatible with Reason out of the box -- so it'll be possible to build unikernels from a slick editor interface quite soon hopefully!