Might the upcoming Papal Conclave elect for Pope Benedict to continue, while electing a successor to be his co-adjutor with the right to succession? Pretty unlikely. It would seem even more unprecedented than a pope resigning, and if it were to happen likely assumed to be the plan all along an detract from the current sense of it being an act of humility on the part of Pope Benedict.If this were the bishop of another diocese submitting his resignation due to declining health, it might not even be though newsworthy. Though even that seems a rather modern practice. In the past the bishop might simply be assigned an auxiliary to help out or a coadjutor to not only help but to succeed him. This is normally done by putting in a request to the Holy See, but the Pope can't ask himself to appoint a coadjutor.
The Diocese of Rome actually has a number of auxiliary bishops. The chief of these acts as the Vicar-General of the Diocese and is Cardinal Vallini. Cardinal Vallini formerly held the position that Cardinal Burke now holds as the Prefect of the Apostolic Signatura. Though these auxiliaries function mainly on behalf of the diocese, and not in broader events. The pope would not likely use one of his Rome auxiliaries to represent him at an event like World Youth Day or any other foreign travels, and not even particularly for Papal Masses such as Holy Week and Easter Sunday.
On the other hand, if there were a coadjutor with the right of succession to the papacy he would have the added prominence that might allow him to represent the papacy at such events. Perhaps Pope Benedict might have asked for a conclave to be assembled to appoint his successor as a coadjutor while he continues to hold the office? There are no rules for calling for such a conclave. Conclaves are only called to name successors when the papacy is vacant. It might have been considered even more unprecedented for Benedict to set up new rules and called a conclave to name a coadjutor to succeed him. Though once he has renounced the office, it would seem possible for the conclave to consider it while asking him to continue on. Unlikely at this point, but certainly something they could consider.
