The number one way that would happen is if people are using bitcoin and cryptocurrency. THEN governments will adopt it.
Bitcoin adoption is good. But government adoption is not necessary and it contradicts the goals and objectives of bitcoin as a decentralized technology.
For mass adoption as a currency, the issues of volatility and scalability; lack of it, has to be resolved.
This would propel merchants to accept bitcoin not for it's speculative value, but the ease of making transactions using the blockchain