I would suggest that it was the broad outline of the same ending he planned and shared with DnD just implemented badly. He's probably more pissed that they made his ending so unpopular by completely botching the landing as he now can't use that same ending without risk of rejection. I still maintain it would have sucked as an ending even if it had been implemented at the same standard as series 5, but what we got made it far far worse.

The reason he hasn't finished (or isn't even trying any more) is because he's written himself into a corner. There are a lot of loose ends and parts that don't make sense, and that's not even counting the parts that the show left out!

He probably felt dread, because he was probably hoping that they'd fix some of the mistakes he made, and make writing the book simpler.

He probably couldn't see the tv due to the big pile of money sitting between him and the screen covering his view.

I think he was fine with it, watching from his hot tub filled with money.