Currencies are a medium of exchange and the largest medium of exchange used become money. So it makes sense to cater the currency to the global audience. This will allow users from separate corners of the world to transact between themselves without issues like foreign exchange rate differences. The bigger the market of people that transact between themselves, the bigger the division of labor and the productivity of people.
For me it doesn't make sense to limit a currency to a specific geographic area. Economic, social or political differences are not important when using money.
One reason for limiting the currency - or at least cater specifically - to a geographic region or certain group of people, is the belief that it will speed up adoption (because its a problem-solver). But I guess in the long run, the currency would have to cater to the global audience anyway. So I guess its best to design one that caters to everyone (I'm not sure if it's possible to make everyone happy, though).
Then, does it have to be as simple as possible, or full of features?