Capcom's Street Fighter IV will not be adding any new characters to its roster anytime in the near future, in an effort to maintain the core game's relevance.
While Capcom has already released two downloadable content (DLC) packs for Street Fighter IV, with the first being "Championship Mode", where players compete for points and ranking, along with the ability to record and vote on matches. The second DLC pack was five sets of alternate costumes for characters, and later on a value pack of all the skins.
In a recent interview with Gaming Union, Seth Killian, Capcom's Community Manager, revealed that Capcom has,
No plans for additional DLC right now. We want the core game to be a completely functional package, and character DLC could split the user-base.
Players can probably expect more DLC like the above, as they donít affect the gameplay; just not anytime soon. However, there are no plans at all to add characters such as Dee-Jay and T-Hawk to the rosters.