Shae is a great pick. I've been stuck on their focus on her peculiar characteristics and mysterious past and think she is a deeper player, but it really could just be that she's being used to spark Tyrion's rebellion.

Still, I doubt it. I just do not think Tyrion will betray his family. Who is he going to betray to? Even if he goes to the Starks, he will lose most of his status since it's the Tywin Lannister name that keeps him from being just a worthless imp to everybody. Furthermore, he'll forever be known as a traitor. Even if your family sucks, you don't betray them and get thought highly because of it.

Tywin chopping off Shae's head is an interesting proposition, though. It allows for Tyrion to try to hurt his family without explicitly betraying them. Like he might plot to kill his father, but do so in a way that doesn't kill the family, in a way that nobody knows he's a traitor. I could see Tyrion pulling a Littlefinger and tricking everybody inconspicuously