If Pao could sue KPC&B, I think he stands a chance, unrelated as they are, it suggests suits can go forward on slim allegations and here he has evidence clear as day they fired him for having a difference in opinion on their hiring practices. He personally didn't discriminate nor personally conduct himself untowards anyone. He offered some (unconvincing evidence about how women don't have the same aptitude as men --but you are likely to find evidence Google does have internal hiring goals and allows a culture which virtue signals against the majority culture) and they didn't like it.
Thing is, if this had been a woman or minority citing some dubious data about how more women and minorities should be hired (which I agree with but on other principles), we would not even blink at it, if it even would have surfaced)