My favorite bit of foreshadowing that at the time seemed like just a throwaway quip was Butters' line in Ghost Story telling the Einherjar that he wouldn't be getting into any sparring rings until he had a functional light saber.

Q: How do you forge a weapon?
A: You heat the raw material to just short of the point of destruction then beat the hell out of it with a harder, heavier object to shape it into the desired form.
First Justin and HWWB, then Lea, then the White Council and/or Wardens were (theoretically) manipulated into being the hammers that pounded Harry into the desired form.

If there's a guiding hand behind the events in Harry's early life, the person behind this theoretical plan isn't protecting Harry because s/he is using the same underlying logic that Lea uses to explain the harshness of her training methods with Molly in Ghost Story.

As soon as I read the big revelation in Skin Game that the Genoskwa was in possession (or possessed by) one of the coins, I've been hoping to see a battle between the Genoskwa in full Denarian mode and River Shoulders wielding Amoracchius.

My WAG:
Rudolph will beat the rap, Harry will go vigilante on his ass, thus bringing him into conflict with the White Council.

I think Jim will go a different direction. Throughout the series Harry has depended on slinging ever-increasing amounts of power, but has always admitted that delicacy and subtle uses of power are the areas where he is most lacking.
My WAG for Mirror, Mirror is that whatever the situation is, it will require the focus and control of a neurosurgeon's scalpel, when Harry is most suited to and most used to wielding the equivalent of a chainsaw.

Maybe it's just me, but isn't there a blindingly obvious solution to Thomas' condition that Harry is in a unique position to be aware of?
Harry knows about the situation between Irwin Pounder and his white court fiancée Connie. Irwin survived the first encounter when Connie's hunger awoke, which previously was inevitably fatal to the victim, and continues to be fed upon without ill effect.
So why doesn't Harry call in River Shoulders and his kin to see if one or more of them can feed enough energy to Thomas to stabilize him without endangering anyone's life? The Forest People can handle the drain without serious risk, even with Thomas' hunger in the negative feedback loop it seems to be stuck in.

Just to note, as soon as I saw the Huntsmen explained, I thought "Chronicles of Prydain!"

I had the same thought.

Where does Christmas Eve fall on the DF timeline? Before or after Skin Game?