Sorry, but this has several flaws.
First off, you yourself admit if the song is long enough. Well, what if the song chosen is so short that it only has five lines?
Secondly... Asking all people who want to participate within the first song/round of play, that'll just eliminate a lot of potential future players. One thing games here should have is the ability to allow people to join and play at whatever point possible within the game specifics themselves. For instance, Hensonville does allow for people to join up practically almost year round. Yes, applications have to submitted, and those applications have to be approved first, but we allow for people to join throughout almost the entire calendar year.
Third, if you say that a player's out if they post the last line of the song, that's just going to get rid of a lot of players as well.
Unless the rules are better structured, I'm going to have to say no to starting a Muppet Musical Chairs thread.
Hope you understand and have a good day.