No idea. At first I thought she would be the epilogue POV (and we all know what happens to those... /wink.gif' class='bbc_emoticon' alt=';)' /> ), but I think it's now confirmed that she's a real POV, so I don't know. Maybe her POV won't reveal her plans somehow? If there's any author that could pull that off, it's GRRM.
Personally, I think that, like Ned Stark, it will be possible for Mel to give some stuff away while keeping her secrets. In particular, her manipulations of Stannis, her sexual relationship with him, and how she came to dragonstone and decided to support him in the first place will be will all be made clear. Also, what she feels her exact role in the upcoming war will be. However, I think any arcane knowledge she may possess of the others and their exact history and mission will be kept under wraps.
Also, I can't help but suspect that, rather than becoming a regular POV, Mel will simply have one crucial chapter in which we get inside her head. I think it will be the one in which she betrays Stannis somehow to defect over to Jon's side. Since we all know that Stannis is not Azor Azai, I'm sure Mel will become coninced that Jon is the true chosen one, and dedicate herself to him completely. (However, she'll know better than to inform Stannis of this straight off.)
The thing is, I think that near the end of ADwD, Stannis may well become desperate and attempt to betray Jon somehow, and take the lands, castles, or men rightly sworn to the nights watch. We've all already witnessed the fact that Stannis can convince himself that anything he does can be justified under the right circumstances. And I think it's safe to say that, by the end of ADwD, he'll be pretty dang desperate indeed. By the end of AFFC, as Jaime Lanister notes, the Lannister's have all but one and Stannis has hopelessly lost. They have captured Dragonstone, and the North has no intention of uniting behind Stannis. And if Stannis shows his usual charm and diplomacy in dealing with the mountain tribes, I think it's safe to say that exactly 0 men will agree to agree to fight with him. So, by the end of the book, Stannis will probably be desperate enough to do just about anything-- including betraying and/ or killing Jon Snow, and taking the land, resources, and castles of the nightswatch for himself.
He'll probably return to the wall near the end of the novel and reveal his plans to Mel, whom he still believes is his #1 ally. This is when we'll get into Mel's head, and she'll reveal that she is now loyal to Jon, not Stannis. She'll probably save jon from being betrayed by Stannis, yet another one of his enemies. (It would make sense in relation to her predictions to Jon that his greatest enemies yet were the ones he was not aware of, and did not think of as enemies.) When he realizes he's been betrayed by Mel, Stannis will probably break like brittle iron, and proceed to burning his daughter to wake the stone dragon or some similar attrocity.
Sorry, I've gotten off topic with my crazy predictions. My point is, that Mel will reaveal more to us about Stannis and his motivations, as well as possibly giving us some more hints about the others and the war for the dawn.