Mario & Sonic at the Olympic Games, but of course they would. Wouldn't you, if your game was one of the best-selling games on the best-selling console? Not even Sonic Team would botch that decision.
This purported scan from Nintendo Acción magazine teases a new Sonic and Mario title with the following text (as translated by Sega Nerds): "Who are these two and why do they come to see each other? Find out all the details on the mystery game in the next magazine. But before that, here are some clues: Games, Olympics, Cold, It's winter..."
Either this is a super obvious hint of a Winter Olympics-based sequel, or a fake magazine page, or intentional misdirection from the magazine.