The EPR gedanken experiment was invented by Einstein Podolsky and Rosen in 1935. It involved positions and momenta. In 1957, Bohm revised this gedanken experiment into one involving spins, or polarizations. In 1964, Bell analyzed this experiment and showed that it implied nonlocality (or defeated hidden variables) by a finite margin. Soon thereafter, the EPRBB version of the experiment was actually performed many times, with results supporting QM.
However, the original EPR experiment involving position and momentum remains an unperformed gedanken experiment, as far as I know. I can't even find a reference to a failed attempt to perform it. Why is this? Will we ever be able to perform the original EPR experiment?