The FAA's notice said that studies indicate that wakes generated by 747-8 and 787 models—essentially cones of spinning air spreading out from the tip of each wing—"may be more substantial than those" created by existing wide-body or jumbo jets such as the Boeing 747-400 or Airbus A340.
Isn't understanding this sort of thing on each type what flight tests and FAA certification is meant to be all about ?
And if the caution is with aircraft under test, before these issues are fully worked out, shouldn't the restriction be a standard procedure for all experimental types of this size, not just attached to a specific type ?