This article, originally from USA Today examines the number of bishops’ offices vacant in the US. I think some of article’s numbers might be off, but Canon lawyer Ed Peters has a list at his site.
In any case, a number of vacancies and potential vacancies (diocesan bishops serving past age 75) will need to be filled soon. The article says 37 bishops’ offices will need to be filled by the end of the year (including auxiliaries), but only five sees are canonically vacant and another 14 will have bishops still serving past the age of 75. Filling an auxiliary’s office is not as critical as filling the ordinary’s. It’s not a crisis, but it’s something to think about.
Of course, it may not be a lack of suitable candidates, but that as the Pope gets older he’s sees less and less reason why his brother bishops can’t stay on past retirement if they’re healthy.
Or, my hope, the Vatican is fed up with the recommendations the US bishops’ conference has been sending them (think Palm Beach, Florida, where two successive bishops had to be removed for abuse before O’Malley showed up) and keeps sending back the ternas and asking for better ones. (The terna is the list of three names that the bishops’ conference forwards to the Congregation for Bishop as recommendations for filling a particular see. The Congregation then picks one and recommends him to the Pope who then approves it (most common), rejects it, or picks someone else he wants (very rare).)
Have you noticed how many of the bishops do not fulfill the canonical requirement for a doctorate?
Probably because there are probably two or three and sometimes as many as a dozen new bishops appointed around the world everyday. The Pope doesn’t have the time to interview each one personally (which would take a couple hours each if you’re going to be thorough.) That’s why this system was set up in the first place.