Out of the entire Street Fighter II Turbo cast only two fighters didn't make the transition over to Street Fighter IV. Those of course are Dee Jay and T. Hawk. According to the games producer, Yoshinori Ono, character models for both combatants were created, though never finished.
Furthermore, IGN states that T. Hawk even had his move set planned out for battle, though Ono-san neglected to divulge a reason as to why the two were not included in the latest addition to the series.
Thankfully, however, Ono has said that if enough fan interest is shown in regards to the two characters, Capcom may release them as downloadable content down the road. If you're a fan of either fighter, now is your chance to be heard!