Britney Spears write a song? Ha! That's a good one. She couldn't write a good song if her life depended on it. As far as Spears being “rock”…are you sure you are listening to Britney Spears? Just because she has a guitar or whatever in the background doesn't classify her as rock. Puff Daddy rapped to the beat of Kashmir by Led Zeppelin. Does that make him rock? She is about as pop as you can get. The only real reason people saw her movie is because she is pretty hot. I don't mean to sound like an @$$, but I really don't think she would fit as a GB. She doesn't have the look or anything. She's just not a GB.
Going on that, I think it would be difficult to find ANYBODY who could actually live up to the roles of the original guys. They are the only ones that can play a Ghostbuster like it is supposed to be played. It's not just the look, but the feel of the character. The super intelligent, yet normal person mentality is tough to find. Almost everybody that was named is too Hollywood. The original guys were just normal people, and sadly there are not many normal actors in Hollywood right now. A super model looking Ghostbuster just doesn't fit the mold. They'd have to dig down to find somebody that is young enough to be the age they want for this new breed of GBs, but they aren't super good looking pretty boys. Just a bunch of normal Joes. I can't think of anybody right now that would fit. They'd almost have to be complete unknowns because almost all of the big, young stars in Hollywood are “pretty boys”.
-BruceLee