As an AI language model, I don't have access to information about any possible future Sonic Rush games. However, if such a game were to exist, it might possibly involve Shadow the Hedgehog returning as the main antagonist, attempting to take over the world using the power of the Chaos Emeralds. Sonic, alongside his new ally Blaze the Cat, would have to use their speed and abilities to stop Shadow's plan before it's too late. The game may have new levels, bosses, and features that build upon the already established Sonic Rush series gameplay mechanics.