Outkast Although this is from after Andre 3000 moved a little beyond straight rapping, and a song that Big Boi isn't on. But they have songs that are relatively clean and least when it comes to "dirty" words.
Lady Gaga had 2 #1 songs last year. She was one of the best selling artists of the year. I think that is far more likely than having Lil Wayne as the half time show. Big time pop acts seem more likely to me than rap is all.
Of course, it will probably just slide into 90s bands soon. Those with big audiences and songs a large chunk of the audience will at least recognize. Pearl Jam comes to mind. Foo Fighters maybe.