Absolutely it can br tracked. That's the benefit of having an open ledger system in place. We can track each and every transaction.
Coming to how it would work as a global currency, I believe if BTC becomes the global currency, it would become much more stable and also there needs to be certain regulators in place for BTC. Also, the value will sky rocket as governments would stock more Bitcoin and as we know its a deflationary asset (with limited supply), the increased demands would take BTC to unimaginable value.