I know I'm swinging for the fences with this one, and GRRM would really have to pick up the pace with these last two books to make it work, but I think the eventual king could be Littlefinger.
Hear me out, this dude has either killed or played a MAJOR part in the deaths of Jon Arryn, Ned Stark, Joffery and Lysa Arryn. These weren't exactly peasants he was knocking off. I think GRRM has been showing us from the beginning not to underestimate Littlefinger. As Varys said, "Power goes to whoever the people believe has the power." I think by marrying Sansa to Lysa's son, and a couple of more moves here and there, he could control the North, the Vale, and eventually King's Landing.
I think Sansa is gonna take him out on some "the student has become the teacher" type isht.
Everyone has his or her weakness and Sansa is potentially a very big weakness for Littlefinger. I'm like 98.9% sure this is going to happen so I'm looking forward to it. I don't know that it will end up with Sansa becoming queen of Westeros, I doubt it (I think that title will ultimately go to Dany, hence my screen name), but I think Sansa will eventually be the key to the restoration of House Stark, which is fitting because she was pretty much the catalyst for its downfall.
As for Ice and Fire, I'm confused. I thought a Song of Ice and Fire was just a personification of Jon Snow (since he has both Ice & Fire blood), but I'm think its could also be Others vs. Dragons, because I think the dragons are the key to getting rid of the Others.