I believe the nanosolar which have a higher output efficiency, lightweight and flexible become widely available, it possible get longer flight time from nanosolar feeding to a MR battery giving it an extra time before it exhausted but I doubt we will ever see a MR run entirely off solar alone without a battery.
This new nanosolar is being test right now and I believe it not too far off before it become available to public. It come in a roll of sheet and you can basically apply it on anything.
Bill