I don't think it's gonna be Britney, I don't even think it will be Mariah or Madonna.
It may be someone we don't expect.......unfortunately, that doesn't bode well. It could be someone ala Soulja Boy/Sean Kingston or something along the lines of a T-Pain/Akon thing.
Personally, I'd like to say Vanessa Hudgens as well even though Tim randomly threw that out there.