They also need people who are big but not HUGE. Yes, Carrie Underwood is really big, but she's not Adele, Lady Gaga, Katy Perry, Beyonce, etc in terms of worldwide popularity at the time she signed in to do this. I wouldn't be surprised if we saw their next show built around one of THE VOICE coaches, particularly Usher or Christina Aguilera.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"