After watching Sweeney Todd, I can come to only one conclusion: Across the Universe needed a lot more slashing at people's throats with razors.
Musicals always have the difficulty of being taken seriously, so making a horror story into a musical is the only logical solution. I suddenly have the desire to see Evil Dead the Musical. The film was ridiculous, and musicals are ridiculous. It's kind of the equivilent of "two wrongs make a right".
I was also very impressed by Alan Rickman's singing ability and capacity for creeping the hell out of me. I propose another film make the transition to musical, following the success of The Lion King, Spamalot and Evil Dead. Die Hard the Musical.