A centralized entity adopting a decentralized system? Not going to happen.
For Bitcoin to be a global reserve currency, it first has to be accepted as legal tender and no country owns Bitcoin so no country can make it a "global reserve currency". Different countries have to accept it individually first.

I don't need Bitcoin to be legal tender, I just need the government not to be against it so people who want to use it can use it freely without any limitations. If it's not legal tender but people are free to accept it if they want and the government is not against it then I don't see a problem.