The results mean that Serena will play Wozniacki in a reprise of the 2014 US Open final (won by Serena) and Radwanska will play Halep. I suspect we will see a Williams-Halep final, although I would not be surprised to see a Wozniacki-Halep final (or even Wozniacki-Radwanska) instead. Serena having clinched the #1 ranking probably does not care too much about winning her 3rd consecutive year-ending championship. If Serena does make it past Wozniacki (which is more likely than not, then I suspect her match with Halep will be very different from the 0-6 2-6 drubbing she received earlier this week).
The surprise of the tournament was that the power hitters of Petra Kvitova and Sharapova failed to make it through the round robin section to the semifinals..