The funny thing about negative interest rates is it is one of the few good reasons to buy physical gold, especially with the elimination of large denomination euro notes.
All gold is IMO is a hedge against inflation by tying your monetary policy to the rate at which you can dig some shit out of the ground. Not remotely sane IMO.
It would be like basing the value of the dollar on corn. At least corn would have some real value though (fuel, food, etc.).