An interesting question indeed. I would not trust anyone as a custodian of my gold or silver though. Keep it close to my chest.
As they say with Bitcoin, if you do not own the private key it is not yours.
The same goes for gold and silver IMO. If you do not have it in your hands what do you have?
What do you have if you DO have it in your hands? Are you going to melt it down and use it in building your own electronics? Are you going to make a plate with it to sanitize your dishes, or are you going to use it as jewelry to inflate your ego and increase your potential of being mugged? Are you going to use hunks of gold to barter with if the economy were to collapse... With bitcoin around there is limited use for Gold, other than the few utility options it may have (though there are better/cheaper alternatives to any of its utility).
"Are you going to use hunks of gold to barter with if the economy were to collapse... " <---- This one. For everything else, there is Steem Dollars! =)
Private vault services are advised for people with large amounts however.