Nick Jonas is this close to be a judge on American Idol. He and Pharrell Williams are close to signing deals which would mean that Randy Jackson would be giving up his seat. I think these are two good choices. I think they would be great choices if not for Mariah Carey.
Mariah is going to overwhelm these two. Pharrell would have to be the bad guy/Simon Cowell role. Pharrell is an awesome talent but one of the reasons he stays in the background a lot is because I don't think he wants to be always front and center and I'm not sure he can stand up to Mariah. Nick will do whatever Mariah wants because he will always feel he is lucky to be there and have a job and getting paid for it. Think of him as a younger Randy Jackson.