I believe Rollo's past should be revealed soon. He must have gone through tragic past. Next who is his contractor. V.V's likely.
I think Rollo could have met Lelouch when he was still a prince once. That explains why Lelouch didn't remember Rollo but he left a big impression in Rollo that he admires him, perhaps saved his life unknowingly. Lelouch may think it was nothing, but too Rollo, it's very important. If there is a photo in his locket, will the photo be him and prince Lelouch?
If Rollo had endured harsh life before his job in supervising Lelouch, over this one year, he would have softened. He like being his brother. Unfortunately things won't go his way. He knows one day he have to kill him when he regains his memory. But, this one year of interaction will certainly affect him, he will most certainly deflect and very likely he will sacrifice himself somewhere down the road for Lelouch's sake. Obviously, he will be happy. By then Lelouch will really accept him as his brother. Not a fake brother. Those memory of the one year is real even though Lelouch's memory was altered to make him believe that Rollo's his only brother. The one year event really happened, not implanted to them.
His geass will power-up or becomes permanent. I hope this will not be the end of Rollo if it happens.
I certainly hope he survives the series, living with Nunnally or even with Lelouch as a happy family. After going through so much, Rollo deserve to be loved.