Is there a hub gear that can be disengaged? When maneuvering a folded bicycle the pedal cranks turn when drive wheel rotates backwards causes difficulty. Do any hub gears have a gear disengage facility to overcome this problem?
Old, plain, one-gear Velosteel-like hubs had this feature thanks to using rollers instead of cogs, but I suppose it does not meet your expectations.

If you REALLY need this feature you can modify Shimano Nexus 3 to obtain what you want by removing four cogs from part no 4 shownhere. You will lose 1st gear, rest will work as before.