[In fact, there's something very Flannery O'Connor in his imagery. Read her short story "Greenleaf" published just after her death from lupus.]
I've known people, including family, who profess to never sin or have no need for a Savior. How to get through to such people? [May Jesus "stab them in the heart!" See: O'Connor above.] It's frustrating. I believe the pope is expressing a similar frustration.
That said, I think the pope should be more careful in his public utterances. He's not an assistant pastor in an obscure parish back of beyond.
I give him enough credit to take him at his word. If he had wanted to express "frustration" regarding the supposed blindness of those he judges as particularly spiritually lacking (the "pelagians", "restorationists", "ideological Christians", "museum mummies", "slaves of superficiality" to name a few of the choice insults he has flung at practicing Catholics) he is obviously quite capable of making his point. So when he says he prays for such people to "fall", I believe him. Rather than recommending prayer and fasting for the advancement in the spiritual life of the souls under his care, he tells us that he prays for them to sin. He himself has stated that his homilies are part of his "magisterium", but his banana peel prayer has no foundation whatsoever in Catholic theology. And in making sweeping judgments regarding the spiritual condition of others based on externals, he is selectively applying his own "Who am I to judge" philosophy.