We use OpenAPI for my company's internal docs. ACMEv2 is at least partially covered in there by us. If a public project were to exist then I think we'd be interested in participating in it.
While the RFC is nice and all, I think having a more structurally-defined spec is beneficial to make sure the spec, and its implementation, are well understood.
Keeping this moving, @ahaw021, is there a repo you know of that contains a good attempt at the OpenAPI spec for ACMEv2? Or, are you able to put the stuff you've worked on so far in a suitable location with an appropriate license?