Regarding regulations for approval of unusual aircraft, the FAA is chartered to test and approve, and will derive appropriate requirements should an unusual aircraft be proposed that does not fit into an existing catagory.
The Fly By Wire Boeing 777 does not meet the "normal" FAA standards for handling, so the FAA and Boeing agreed to a set of "special conditions" that defined the maneuvers and measurements that assured safe and effective controls.
I don't believe lack of specific standards is much of an impediment, as long as the applicant (that's the manufacturer) has nailed down the special conditions prior to betting the future of the company on the certification.
