The notion that the readiness potential acts as an unconscious cause of spontaneous activity has come under severe fire. Most notably, it also occurs as a random fluctuation without causing any sort of action—it’s just the sort of thing complex systems sometimes do. What rather seems to have happened in the Libet experiments is that it acted as a sort of symmetry breaker, something that tipped the scales in a brain already poised to make a decision, and enabled the translation of that decision into action. Think of it like one of these paternoster lifts, where cabins are continually carried up. You stand outside, waiting for the next cabin to pass, and enter it to move up; but even though one could detect that cabin going up before you use it to ascend (to bring a decided action to bear, in the image), that doesn’t mean that the paternoster cabin is what caused you to do so.
This is borne out by experiments in which the neural activity of probands that are instructed not to act is compared to that of people that do perform some action at their leisure:
To avoid unintentionally cherry-picking brain noise, they included a control condition in which people didn’t move at all. An artificial-intelligence classifier allowed them to find at what point brain activity in the two conditions diverged. If Libet was right, that should have happened at 500 milliseconds before the movement. But the algorithm couldn’t tell any difference until about only 150 milliseconds before the movement, the time people reported making decisions in Libet’s original experiment. [source]
So at least that particular signal does not seem to grant the ability to predict actions before you’re aware of them.