I really loved Fr. McCue's back story as well. The canon character is such an example, IMO, of "no small roles" -- he doesn't show up often or have many lines, but it's clear that he has a long, deep connection with the family, especially Margaret. The history that Aloysia envisions between them strikes me as really plausible for their generation's experience of Cold War Catholic America. (Yes, there are many women in my family of whom canon!Maggie reminds me, and Aloysia's version strikes me as very canon-compatible).

"I believe, based on my PET scan results, that it would be best if I were in a state of grace."
I don't know if any fan writer has ever come up with a line I find truer to Scully during the cancer arc. If one sentence could ever encapsulate a character...