One of the reasons I did not incorporate it on the radial, was that the radials have a (near) constant crankcase volume. Singles and boxers have a strong pulsating crankvent, meaning that the oil gets "atomized" in the rockerbox(es).
The radial has a steady flow, so I expect issues with too much standing liquid level in the rockerboxes. It is no biggie, the radial makes very few running hours, so....