I quoted that line to Magnocavallo.
"Ah," he said, "but that's the problem. What did primacy mean in the first millennium? Getting people to agree on that is going to be difficult."
There is that issue again; the lines of authority, made more acute since the Pope has assumed so much authority in relatively recent times. My guess is that the authority of the Pope would have to be elaborated upon, for any of this to go anywhere.
Benedict knows that Papal authority is at the center of the rift between Catholicism and Orthodoxy, yet he continues to insist that "concrete actions" are all that matter.
Things will get interesting in the next years. If he makes the trip to Russia, it will mean that he will have convinced the Russian Orthodox that he is serious about reunion.