I'm still holding out hope for returning teams from the earliest seasons. Specifically: Ken & Gerard, Colin & Christy, Linda & Karen, Kris & Jon, Lena & Kristy, and the Gaghans.
And if they ever do three-peaters again, my only choices would be Dustin & Kandace and Oswald & Danny. These two teams have been amazing on both of their seasons, and being from an earlier era should not be a hindrance from asking them back!