Nope. I very doubt government will want to relinquish control...
As a sub currency it could gain mainstream use but i think there will be much blood before BTC replace the Dollar.
Yes, I do agree with you. The government won't allow BTC to replace the current national currency as they won't be able to impose taxation on BTC and won't even be able to control transactions, due to BTC's decentralized nature.
However, I do think that it has started to gain some mainstream usage, what with tech giants like Dell and Microsoft accepting BTC, and the more this adoption increases, the better for us and BTC.