Better worldwide economy
The world will expand back to the one time size of the British empire with the Saudi and Kuwaiti oil under its soil.
It will never happen. Look at Europe!
for the whole world to have a single currency, you need synchorization of central banks of very country, the concept of forex reserves will be obsolete, not to mention, it will assume whole world is going through the same economic conditions.
That would be bad except for the poor irresponsible countries.