$7,333,755,829,104

Yep - That's trillions Based on current spot gold price of  $1,222.84

http://onlygold.com/Info/All-The-Gold-In-The-World.asp

If there is one thing to make to barbaric relic to go away it will be Bitcoin.

Gold market cap / Bitcoin market cap (minus 1 million BTCs lost) => ~ 366 000 USD per 1 BTC

Yes $500k per 1 BTC doesn't seem unreasonable in next 15 years or so. Even today (I mean right here, right now) with all the problems Bitcoin has (and there is plenty - such as it doesn't scale well) it's already superior to gold so I don't see a reason why it shouldn't be on par with gold.