Bitcoin is already a global currency. You can earn it, spend it, save it, invest it.

Invest globally with bitcoin. Wealthfront for bitcoin.
http://themerkle.com/bitcoin-investment-startup-keza-unveils-ios-beta-app/
https://www.producthunt.com/tech/keza
http://getkeza.com/ (It's free to apply for a Keza account)