Capcom's community manager, Seth Killian, was asked if the company will be conducting a character poll for Super Street Fighter 4, like they one they did for the first release of the game, where they added the fighters who got the most votes, here's what he said on the issue.
Seth: We've discussed a character poll, and it's not out of the question, but the question is whether or not we have the development time available to follow through on the results.
There's a much smaller window of time for this game between announcement of the title and when it actually ships, which means less time to create a new character given how many we're already adding.
Source: Unity Boards.