I can never see Bitcoin being accepted for use officially alongside any major fiat currency. There may be certain countries who have fairly small economies that accept its use, however that will be the extend of it. Governments want control (via central banks) of their own monetary policies and that becomes impossible if you are using a currency where you cannot expand the supply if it is required. Every country in the world loves being able to depreciate their own currency because it makes any debts owed cheaper to service and allows them to export goods to other countries for cheaper - there is a constant battle between major powers to devalue. Besides all that Bitcoin simply does not have the processing power to cover all the transactions required and there are options that allow for instant settlement which will always be preferred. It has a useful purpose - moving larger amounts.