First, any one of the players could do this whether a player association is formed or not. Second, the top players probably make 75% of their prize money from WPA sanctioned events. Why on earth would they give that up just to make a political statement? I'd be surprised if there was even one top player willing to make that kind of sacrifice.
You may recall Stu that professional players did exactly that in 1964 when Cisero was barred from play because he was black. That picket, and Cisero's resulting world championship, is one of the high marks in pool history.