If anything, I've been more convinced that Narishma is tied to Callandor, and will take this weapon up and continue some mission that Rand won't be able to accomplish. He's already held Callandor and of all the Ashaman, we know that Rand trusted him, Damer Flinn and Eben Hopwill (now deceased) to do what he told them to do.

Min thinks Callandor is important, but really hasn't been able to come up with a significant reason what it can offer to the act of locking the Dark One outside the Pattern. I think this may be because it won't be used directly, but will be important to his allies.

I think some of the ambiguity lies in the fact that Logain was also destined for greatness, while Narishma is also marked for something. Perhaps he will defend the Aiel who resort to the Way of the Leaf before Tarmon Gaidon starts in earnest?

I don't think Cyndane/Lanfear will turn towards the Light. I do think that it is possible she will be instrumental in defeating the Dark One because of the way she was punished, but I think she is completely focused on revenge against all parties.