I never thought of it that way but probably they could devise a system where the auxiliary Bishop serving for a long enough time or when the nuncio sees it fit, request the Holy Father to reassign the Auxiliary as a Coadjutor.
My neighboring diocese once had been Sede Vacante for 5 years. Before my current bishop, we were Sede Vacante for almost 2 years. Are there that many Bishops or Bishop Candidates being juggled by the Congregation for Bishops?
I am very acquainted with how Bishops are elected in fact, we, in the diocese almost thought that the Chancellor might be ordained but the new Bishop was the old Chancellor and at the time was the Auxiliary Bishop of our Metropolitan Archdiocese. Who knew?
I think that your last part effectively illustrates the complexity of the appointment process. One never really knows what is going to happen until it does, as there are many variables. I would disagree with another poster’s assertion that auxiliary bishops are necessarily “ordinaries in training.” That is sometimes true, but sometimes it is not. Much has to do with the age of the bishop at the time of the appointment, and how his episcopal ministry plays out. There are many auxiliary bishops who remain so for many years, even decades. (Bishop John Ward of Los Angeles comes to mind, where he was an auxiliary from 1963-1996, or Bishop Patrick Ahern, auxiliary in New York from 1970-1994. Two of the current auxiliaries in Chicago are nearing their 20th anniversaries as bishops, and two others are around the ten-year mark.) Some of these do not desire to have their own dioceses, or for whatever reasons are not seen as desirable candidates. It reminds me of assistant principals in schools. Some want to become principals, while others do not.
A final factor is the fact that, while not always, auxiliaries typically were priests in the same diocese. This gives them a familiarity with the diocese as they begin their episcopal duties. However, most often (again, not always, but usually) an auxiliary who becomes an ordinary does so in another diocese. This gives him a different perspective, especially if his new diocese is smaller than the one in which he served as an auxiliary. if he is to become an archbishop, it may be back in his own archdiocese, or it may be somewhere completely new. Sometimes archbishops of the largest dioceses (the ones where the archbishop is typically a cardinal) were already archbishops elsewhere, and were transferred. (The traditional word was
translated. Think Cardinal Dolan today, or Cardinals McCarrick and Bernardin ) Other times they were ordinaries of smaller dioceses who were elevated to larger sees. Sometimes a priest seems different as a bishop, and the Holy See would want to be able to see that before making him a coadjutor.
