I don't know if Mariah Carey is such a good choice to become a Stooge:  She's had her prior bouts of instability, far more serious than Paula Abdul's, although since she married Nick Cannon, things seem to have stablized in her life.

From my rock-based POV, Dan Auerbach of the Black Keys would be one of my choices, or even Michael Slezak of EW, who wouldn't be afraid to act as a heavy.  Carrie Underwood would be an excellent choice in my view, even though I'm not a huge fan.  She's still in her 20's, has a big following, and not only does she have a journalism degree, I believed she finished second in her class, so she's no dummy.

I'm betting that AI in its current configuration will bow out after next season at an even dozen.  Why?  The voting system.  They absolutely MUST limit the votes to 10 per person per device, like America's Got Talent.  This season, the average age of an AI viewer increased to 50 years old, and if the show keeps allowing thousands of grannies all over the country to power vote, it will continue to generate the same kind of winner it has generated over the last five seasons, with the possible exception of Scotty McCreery, who was 17 years old and a pure country singer.