I believe that using one currency will not change anything. The poor will have less money, but the rich have more. Simply, the currency will be replaced, but the possibility of earning will not change.
If we will use the only currency then I think the only thing that will get change is the bitcoin and the importance of the bitcoin. In the past the bitcoin is being famous and it is the source of income for me. The currency of the bitcoin is not just the currency but it is the saving and the investing as well so I think it is very good to have so I think if we will use the only one side income.