I think Rihanna could get it, she has such a massive catalogue of hits, and since a big percentage of them are either are others' songs that feature her or her songs that feature other artists, she would have a lot of guests that she could bring out.
Gaga, I don't see it. In addition to her decline in popularity, she's become very niche and really mainly appeals to gay men. Not exactly the Super Bowl demographic. She would give a good show, but even Madonna appealed more to straight men than Gaga.
I think Katy has enough hits (even after just a few years) and appeals enough to straight men that she could pull it off too.
By the same token, the halftime show isn't really supposed to appeal to the male demographic. Often it's used to boost female viewers - will more men watch the Super Bowl because of Katy when they wouldn't have watched before? Nah, they'll all be guaranteed viewers anyway.
