I've thought about this and it is gradually taking shape in the world economy today. As you have said, the world powers would definitely turn to Bitcoin as a national reserve since it is void of third parties to control it.
I remember a country whose assets was seized running into billions of dollars because of the fact that they are in war with another country and believe me, if that assets was in Bitcoin, there would not have been anything like another country seizing their assets as they would have been in control over it.

Bitcoin reserve would be an alternative to national investment in cutting ties with foreign control over a country's assets. Many nations would now prefer to keep their assets under their control rather than in foreign currencies or in a foreign land to avoid seizures or other stuffs which could affect their foreign investments over time. Nations would definitely turn to Bitcoin as time goes on to avoid their economy being controlled by another nation posing as a threat to their growth and wealth creation.