It is being reported by SyFyPortal that this season on BSG that Six will no longer be present in Baltar's head.
"Say good-bye to the Six in Baltar's head," a source told SyFy Portal's Michael Hinman. "As much as we like Baltar having this controlling figure literally in his head, we couldn't keep it up forever."
I've always enjoyed that aspect of Baltar's personallity, but they did tend to overuse it as a plot device. This type of change should have drastic affect of the character. Although, SyFyPortal also reports.
"We all know that [Baltar] can't follow the 'plan' by himself, so he will get another visitor," the source said. "He'll be paid a visit by his own likeness that had been helping [Caprica] Six. It should really make things interesting in the last season as everyone tries to figure out who the final Cylon is."
We'll have to wait and see.