Japan's Street Fighter IV Blog has just posted an announcement that a new sequel is "coming soon."
Presumably, the new game will not contain a V in the title (the Street Fighter franchise is famously stingy with its sequels, after all), but instead it will be a new version of Street Fighter IV. Think Championship mode, with faster fighting, refined gameplay and possibly a new character or two.
While the blog didn't give any information on a timeframe for the sequel, we're placing bets on the forthcoming The Tokyo Game Show. We'll keep you posted with any new developments.