In Joystiq's interview with Chris Sigaty, Lead Designer for StarCraft 2, the question came up again, and the following answer might make upset fans happy again.
We brought back, so far, currently we have the original Jim Raynor, who is the main character, and then we have a few other returns, specifically this character Mengsk who is kind of the opponent or the enemy of Raynor, is back as well. Those are the two that jump out as being the biggest right now.
The rest of the interview is an interesting read on its own, so go check it out.Links
Joystiq Interview - Chris Sigaty interviewed
BlizzPlanet - August announcement