Taylor actually... given how ambitious she is, she would go all out with the production and throw in a country medley with special guests and cater to the redneck/hillbilly America while turning out the pop hits as well. She doesn't need to be a great performer, she just needs to execute that 12 minute performance like Katy did.
Lopez... meh no one would know her songs, she would just be jumping around the stage with several glittery costume changes and do a bit of dancing.
Britney... no words, would be prancing with a whole bunch of dancers doing better than her with the CD recording playing through the speakers.
Rihanna... it would be as sad as her VMA attempts though she would probably run out of breath and couldn't transition from one thing to the other.
Carey... Glittery gown and just standing there with a mic lipping her memorable songs while she has something projected in the background, she might bring out a choir.
