Reading all this got me thinking (related):
What if the betrayal involves Eb setting up Thomas for political purposes of the White Council?
It would fulfill several of these loose ends and cause one hell of a kerfuffle amongst all the parties.
Wow! This makes a great deal of sense to me. It also explains the scene in the trailer when Eb says to Harry, "Boy! Tell me, you ain't dumb enough to try this." and Harry not only responds that he's dumb enough, he pulls up a shield or is drawing up his power. I don't mean that Harry is directly squaring off with Ebenezer, I mean he's going against the plan Eb set into motion.
About Harry not mentioning Nemesis; well, Harry has to be very circumspect about how he brings up this topic with anyone, even Ebenezer. Also, Nemesis isn't the direct threat in this situation. In some deeper discussion about the Black Council it might be worth bringing up, but right now Harry has to worry about who might stick the knife in his back and the person or faction on the Council that is giving them their marching orders. That Nemesis might be or probably is the ultimate string puller is almost irrelevant. Even if Harry knew that; just as an example, Cristos had been turned by Nemesis and was behind the plot against him, Harry can't do anything to Nemesis; at least not yet, he can only move against its agent.
Om the topic of preview chapters; sure, it would be nice if we got five preview chapters, but I remember there was one book where we only got Jim reading three chapters at a book signing that was posted on YouTube and nothing more until the book was released. So even if we only get one more preview chapter that's better than just three.
Disappointment: I really wanted Harry to say to Ebenezer:
"Sir, about the vampire. He's my half-brother,... and your grandson. I thought you should know, if you didn't already" Harry did have enough time to say that much.