According to the Internet in all its various forms, Street Fighter 4 does exist. And it’s called Street Fighter: Battle for the Past. And it features characters from past iterations of the franchise – 24 of them, apparently. Oh, and it’s coming out on Sammy’s AtomisWave arcade board.
According to Capcom, nothing is actually happening, though any announcement is expected to hit the Japanese press, most likely Famitsu, when the time comes.
So you have a title, and some vague idea of platform and characters to be getting on with. For the record, SPOnG believes that the title might be correct, though the use of the AtomisWave board makes little sense, given the profile of the series.
We will, of course, keep you updated.