I think it is possible. Every country has its own financial institution and different levels in that. Removing these flaws by bringing a common mechanism would be the major  problem. Bringing one global currency in to scene, will increase debt on countries having low value currency. For example - Indian Rupee is downgraded compare to dollar and hence such conversion may lead to increase debt level over our country. The bigger a system gets,the more it become prone to faults. Distribution of powers among developed and developing countries would be another major problem.