Wow. I did not see this coming!
I think (hope) this will help the jury if KB's body isn't found. In other cases (Chris Watts, Drew Peterson, Scott Peterson) there was only one person who was directly involved in the murder plot - the murderer.
As long as only PF and KB were involved, he could pretend that she was doing a 'Gone Girl' or that she was just the kind of woman who would walk on her boyfriend and baby. Unfortunately, now there's a very credible person who was involved in at least part of the plot. This really undermines PF's defense, IMHO. He could argue that a lot of it is 'he said, she said' between himself and the 'other woman' in a love triangle. It's harder to argue with the evidence of a phone pinging.
Long shot, but I wouldn't be entirely surprised if PF's lawyer tries to turn it around and claim that KK was the murderer and that PF helped clean up out of a mistaken sense of loyalty to her.
I wonder if PF and KK have had any communication, directly or indirectly (through SF?), since KB's disappearance.