Fortissimo:-
On the airworthiness front, 'suitability for safe flight' depends on the level of 'safe' you are trying to achieve.
Well let's drill down to a less ambiguous airworthiness definition:-
"The ability of an aircraft or other airborne equipment or system to operate without significant hazard to aircrew, groundcrew, passengers or to the general public over which the airborne systems are flown".
I would suggest that all embracing wording would include UAS's, and if you exclude for the sake of argument all except the general public you cannot exclude them. I believe that the original concept of airworthiness was for 'the protection of those wot was down below'. With the coming of the drones time perhaps to revisit that concept.