We currently have a some "simple" drivers here:
They are "simple" in that they don't do anything smart and are very no-frills. They don't hide very much in their implementations which makes them good for forcing certain behaviors in Gremlin Server tests. That said, they kinda stink and are awkward to work with. Would be nice if they were a bit more refined in what they do.
I think they should minimally work in such a fashion where you can send a blocking request (in addition to callback-style one that's already there of course). Basically, it should be easy to send a raw RequestMessage and get back a ResponseMessage.