We've traditionally had non-pure Erlang services at WA for things like backing storage, interfacing with other infra, etc. This is just sort of the natural extension of that. There might be some services which we eventually rewrite but for now it's more "new" stuff that's being built with this. Some things will get published soon-ish, but I can't say more at the moment.

EDIT: The rewrites I mentioned are not WA specific, more Meta which is rewriting a lot of C++ and Python stuff to Rust constantly :p