I am intrigued by the idea of a truly global, borderless currency. Scary idea actually, if you're a government.
Here's a thought on creating a global, digital currency: absent a new country appearing on the world map, one can create a new currency via a payment processor/system at gigantic scale or via a similarly large marketplace.
Peter Thiel supposedly saw PayPal as a potential global currency mechanism, and (again, supposedly) has a similar vision for his investment in Stripe. Amazing business lead by an incredibly smart founder.
I also think Jeff Bezos has a similar vision for Amazon.
I'll back Amazon. Not because I think they do or don't have the capacity to execute, but because global currency standards are a consequence of marketplaces needing to trade beyond their borders. A payment processor in this context seems akin to a solution looking for a problem, which is not to say Stripe couldn't pull it off (their team seems pretty awesome).
So the question then is how does one create a digital marketplace that is so massive that those within its borders can trade not just with each other but also delivers the capacity to trade in physical commodities and/or "real world" services?
Update: I should add there's another very obvious path, being followed by Bitcoin.