We'd like to have asynchronous query support, so reviewing what Microsoft has provided to be extensible is on our list.  That said, we're not clear we can actually make any of the internals asynchronous - so such calls would basically be synchronous but return a Task wrapper so the caller could aggregate them.  That said, we've also discussed doing some internal tweaks to enable pipelining that would take advantage of this.  At the moment we don't see a performance advantage with the current engine so it hasn't made the cut.