Yesterday I managed to find out why the old 3ph plugs have been banned. The pin layout is symmetric. On one side of the plug there's a key "nose" to ensure the plug is always plugged in the right way. If this nose is broken or filed off (can happen quite easily with the later plastic plugs) the plug can be inserted the wrong way round, turning the ground into a phase.
A second reason is: the pin layout cannot ensure the required clockwise phase rotation.
