I don't think it will happen just yet because they all want to preserve their national currencies and have control over money. I do think though each country might digitize their own currencies and use their own blockchain protocols, so they will still own the rights to control the flow of money, unlike with Bitcoin, that is now too decentralized for any one country to govern or control it.
Every country has taking care of thier currency looking up forward for thier economy growth and upgraded technologies. If USA legalized Bitcoin much better they choose the right currency to ruled over this economy as we all know USA is the most improving country, other country has no fear to adopt Bitcoin also.