I really can't imagine most of the pop girls to work well on collaborations with each other. Katy, GaGa, Rihanna all have very distinct tones and textures to their voice which would make all of them hard to blend together. Not to imply that Beyoncι doesn't have a unique voice (the contrary, actually) but she is really good at blending her voice to match others. I think GaGa or Katy would be the worst as features. They'd make it all about them.
