But who would think that mainstream audiences will be so eager to see a movie called "Snakes On A Plane"?
Mainstream audiences aren't necessarily as shallow and dumb as we expect them to be. Something different, like Sweeney Todd, may be just what the modern audiences need. It's guaranteed to have quite a big audience draw with Tim Burton directing and Johnny Depp starring in it. Plus, the theatre supporters are automatically attracted to see it.
On another note, Broadway musicals and the composers are far from being household names. Sad to say, but people around where I live are just now hearing about Wicked. Stories like Sweeney Todd and composers like Sondheim may never be seen or heard any other way by the audiences that this movie has a potential to reach.
Overall, I think it should be a decent adaptation. I'm not sure about Johnny Depp, but I'll give him a chance.
"A bird doesn't sing because it has an answer, it sings because it has a song." -- Maya Angelou