I'm a big, big, BIG Hairspray fan. I adore the original, LOVED the stage version and saw the movie musical 7 times in the cinema - but this is a bad idea. The film doesn't need a sequel. Firstly, the film worked so well because it was stage production before and the songs and storyline was already set - they just had to transport it onto the big screen. Also how can you have Hairspray without Edna? She makes Hairspray what it is! Very pissed off.
Also I doubt Zac Efron would say no to yet another musical. It's his only way of secretly telling us he's 'coming out' without Disney keeping a close eye on him!