PLEASE tell me someone already made a Bagginshield/Boffins Phantom of the Opera AU???? Because if not, I would like to present a Bagginshield/Boffins Phantom of the Opera AU for your consideration.
Christine is OBVIOUSLY Bilbo, he never had much interest for proper singing but ever since his mother died he had gotten a job in the Opera House as a chorus person. She often spoke of the Angel of Music to him, and sang to him before her passing. (Wishing You Were Somehow Here Again is about Belladonna btw).
The Phantom has gotta be Thorin, specifically obsessive/possessive Gold Sick Thorin. His birth deformity is just that he looks really elvish (aka greatly deformed in the eyes of dwarves). Instead of an organ he has a harp which soothes whoever is listening into a deep sense of calm. It's what draws Bilbo to him.
Raoul is Bofur, a presence from Bilbo's youth that wants nothing more than to reconnect. He is kindly and patient with Bilbo and the Phantom, who he believes to be a figment of Bilbo's imagination.
Those are just the main people but I'm sure the other dwarves can fit into the story as well.