The Roman priest Dwight Longenecker has a very interesting and even surprising column about how the Catholic Church could conceivably function with a retired pope and an active pope both calling the Vatican home. His proposal in essence is that the elderly pope would be the quiet, reflective éminence grise while the younger man could be the active global traveler and teacher. The former, "Peter" if you will, could give advice to "Paul" from time to time while both serve the Church in different capacities. Such an arrangement would be a very welcome and concrete reminder that the apostolic foundation of the Church of Rome rests not solely on Peter's shoulders, but equally on those of Paul: both, after all, went to, and were ultimately martyred in, Rome, though Peter is usually the only one to get any attention in Catholic ecclesiology and the Catholic imaginary, which is regrettable--as is the forgetting that Antioch is at least as much a "Petrine" see as Rome is.
This all put me in mind of a little book from 1990, unjustly neglected and deserving of renewed attention: William R. Farmer and Roch Kereszty, Peter and Paul in the Church of Rome: The Ecumenical Potential of a Forgotten Perspective (Paulist, 1990), 186pp.