I think it pretty obvious that Jim is leaving the door open for Thomas. Mab hinted that Thomas would have been a suitable Winter Knight because he loved Justine so much, which was mortal enough for her. Thomas is also a skilled swordsman, so I think it would be an appropriate weapon upgrade for the apocalypse. And of course, Susan wielded Amorachius/Excalibur (Love), so we have precedent of a semi-vampire being wielding the swords. In fact, in the scene where she worries about whether she can touch it without being destroyed, Harry just tells he to swear she will be true to the sword and not commit any evils with it and to be do it for the love of Maggie. And it worked. I don't think the Almighty would have just let anyone wield the Swords. I suspect anyone who does wield them is because they were meant to, and chose to. There are no coincidences around the nails of Christ. The only other candidate I can think of who might use that sword is some reborn King Arthur-type. Marcone might fit that bill, but it would be a dark story line (which actually would fit in with the earliest Arthurian myths - the stories got watered down a lot over time). Harry is the wrong choice, as he is Merlin, not a king. He doesn't want to be and would be a poor ruler of men. Maybe Daniel Carpenter or some other Carpenter...there are not too many candidates off the top of my head.
Esperacchius/Durendal (Hope) would also fit Thomas, if Sanya fell. But I really hope Sanya doesn't as I really like the character. The only other wielders of hope would be someone from the BFG...Daniel Carpenter again perhaps?
As for Fidelacchius/Kusanagi (Faith), I suspect it will stay Butters. He has earned his Sword and his role. And he has a long road ahead. And not for nothing, the Star Wars motif is important. Hence Uriel liking the music (that is no throw away line - it is a big hint about how things work).
And Murphy is a crazy choice. Did you not read the last book? She got basically crippled after using it when she wasn't meant to. If that wasn't a sign, I am not sure what is. And she broke it. I think between the physical, emotional and psychological scars she probably couldn't even if she wanted to. She unfortunately has had her time. I suspect sadly, that she will be killed off next book. She doesn't serve a purpose the way she used to as a character in the early series, and her arc is coming to a close sooner or later. Remember, her and Dresden just worked out they should be together when they have time. Each time, something bad happens to one of them. Harry got killed when they were first about to. There is a symmetry. Jim often says how he has to torture Harry, the book thrives on his pain. And our reaction to it. Believe me, it is coming sooner or later.
