According to a Hollywood Reporter story, Waltz is in negotiations to play an Interpol agent who deals with the Muppets while they're in Europe.
You know what? I'm OK with this. This isn't like Brendan Fraser signing on for an awful Looney Toons movie. Waltz is an Oscar-winning actor who isn't going to sign on for a crappy sequel. While Segel himself won't be back for The Muppets 2, James Bobin is returning to direct. He also co-wrote the movie with Nicholas Stoller, who is responsible for the scripts to The Muppets and The Five-Year Engagement. The Muppets 2 is in good hands.