Andrew Lloyd Webber recently announced Sierra Boggess from Broadway's The Little Mermaid will pair with Ramin Karimloo in the musical sequel to The Phantom of the Opera. The new show entitled, Phantom: Love Never Dies, that will hit London and Broadway stages in 2010. The story is based on the book by Ben Elton with songs by Webber and lyrics by Glenn Slater (who wrote songs for Mermaid). In the sequel the Phantom lures a married Christine away from "a broken-down" Raoul to New York City's Coney Island. Christine brings her teenage son, Gustave, with her.
As exciting as this sounds, I think a musical of Phantom's caliber can stand on its own for eternity without need of a sequel. I fear this might dilute some of its greatness.
I just don't think you can top this (video of original phantom cast):