I'm hoping for a sequel because Platinum was a phenomenal game. Despite the graphical limitations, Game Freak pulled off an ambitious story quite well. The Distortion World was a brilliant idea, Cyrus was a believable villain, and neither the gym leaders nor the Elite Four were pushovers. The story also introduced religion into the Pokemon world which could explored in a possible sequel. The story of Platinum is ripe for a sequel.
Despite his obvious social issues, Cyrus was able to recruit followers relatively easily and his Final Solution if you would was to remake the world in his image. Sound familiar? Cyrus is essentially an allegory to Hitler. A man with a great deal of social issues rises up in popularity with legions of followers who are willing to help him remake the world in his image. Every one of the other villains (except for Lysandre) gave up. Cyrus didn't and stayed in the Distortion World. There's so much to explore in a sequel and it would be a shame to do a remake instead. Then there was that church that I thought was some sort of religion based around Arceus.