I think this cliffhanger confirms that it's a major character. As in Michonne, Maggie, Daryl, or Glenn(Rick and Carl are out of the question obviously)
They wouldn't waste this scene, a scene that comic readers have been waiting for for almost 4 years now, on Rosita, Aaron, Eugene or Sasha. Abraham is a possibility but I don't think it would have the same impact as a character from S1.