At 4:00pm UK time SEGA announced via press release the confirmation of a sequel to Sonic Rush, namely Sonic Rush Adventure. The game recently came under suspicion after a patent application was found by an eagle-eyed member of the SSMB.
With this out of the way I can at last confirm it’s existence. You can find the press release sent in the press release section (within Misc) of the Shadow Depository.
SoE’s Product Page: <a href=”http://www.sega-europe.com/en/Game/571.htm”>http://www.sega-europe.com/en/Game/571.htm</a>