Okay, I'm now jumping into this thread face-first, guys. I think that karma is pretty much a shoo-in, since it's been part of the series from the beginning. Not to mention that the announcement clearly states that "the path the gameplay and story take will depend on the decisions you make along the way".
Now, this could mean a karma system like in inFAMOUS 1 & 2. But I'm really hoping that they introduce a little maturity, along the lines of Footloose's excellent suggestion. It would be exciting to see complicated choices that ditch the simplified explanations as to the consequences of each action. I think we're smart enough to judge good and bad on our own. Not being forced to choose either definite side each time would leave room for surprise.