SIMON COWELL has an interesting idea:  A face-off between all of the winners of the various singing competition shows.

He Tweeted, "Maybe the winner of 'X Factor' this year should compete with winner of 'The Voice' and 'American Idol' in a super final.  Just a thought.  I'd be up for it."  Simon added, quote, "I love the rivalry between all the music shows."

There's no response from the people behind "The Voice" . . . but "Idol" producer NIGEL LYTHGOE has weighed in, and he doesn't think it'd be much of a challenge.

He Tweeted, "The problem is the 'Idol' winner will be a star by then."

If they did this last year, the face-off would be between "Idol's" SCOTTY MCCREERY . . . JAVIER COLON from "The Voice" . . . and "X Factor" winner MELANIE AMARO. 

Who do you think would've won?

Would you watch this show?