But a much better estimation might arise from looking at global consumer demand for Digital Payments. By the year 2020 its conceivable that we are at 1T digital transactions. At an average value of $10 each, we are again speaking of roughly the size of the total market for Gold.
The million dollar question is: What percentage of all digital transactions globally will be made in BTC?
Approaching the problem from the FinServ lens, rather than FinTech, can radically alter your view ;)