What unseen character do see playing a huge role down the line?

[Jamie Lannister]

Lady Dustin

I wonder if she will have something to do with bringing down the Boltons?

I'm more inclined to think she'll be their one loyal ally when the rest of the north wants Roose's head for the RW.

[Child of Spring]

Maester Marwyn, Edric Dayne, Tyrek Lannister and Benjen Stark.

[Jolene Brown]

I wonder about Brienne's father, the Evenstar of Tarth. I don't know about a "huge" role, but I could imagine him doing something that's more of a "pivotal" role in an individual storyline.

Edit - I also think it's a funny title for a non-Dayne. And she mentions that thing about how a woman with plum eyes came to their castle when she was a child and sang, or something like that? It just seemed like a really random thing to throw in. And if she is descended from Dunk the Tall, I wonder if there is some weird family connection to the whole Targaryen part of the story, which I also associate with the Daynes. I'm probably getting crackpot now.

[Richard Rivers]

Mentioned already but the GreatJon

Syrio, one of the few whose death was not seen and is automatically thought to be dead

And Skagos inhabitants, I have a feeling they will be something completely different, like they have a full blown city there or another race of magic people, something unexpected I hope

[Angel_gon]

Awww... :(

But otherwise, I've been expecting Willas Tyrell to show up "soon" since the moment I first read about him.

I'm sorry my friend, but howland reed is at the top of the list of characters we want to meet

[The Meeraculous Third Reed]

Another one I forgot about. Izembaro. I am interested to know how he will "train" Arya further.

[Lord Warhammer]

Osha/Rickon, Benjen Stark, The Greatjon and Edric Storm