Street Fighter 4 has been announced. Capcom did so at a Gamer's Day event in London, and already (as one can see) everyone is buzzing about the news. Committed fighting game sites such as SDtekken.com have already carried the news, and the appropriately named Shoryuken.com has dedicated a subforum to speculation on and anticipation for the game.
It's been eight years since the last SF game, Street Fighter 3: Third Strike, came out and roughly six since Capcom's last original game, Capcom vs SNK 2, arrived which leaves me wondering who is going to be developing this one. Capcom of Japan supposedly disbanded their coin-op division a couple years ago, so unless they're looking to rebuild that empire I can't imagine this will be done in-house, and I don't think they'd farm this out to Capcom USA (although USA is responsible for Super Turbo HD). My guess is that this will be done like Devil Kings, with an outside designer, and then published by Capcom. However, I would love to be wrong.
The other option is to do a console-only release, which I hope they don't do. Street Fighter defined arcades in the 90s, and to do a console-only follow-up in a series arcade-goers have been waiting nine years to play again doesn't make a lot of sense.