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.
I think bitcoin can not replace dollar soon. Because still many people do not know about bitcoin. And there are many millions people who still don't use Internet and than they how can depend on bitcoin. So before the replacement of dollars, there is a urgent need that every person on earth can access the account and they should have a basic knowledge of Internet than they can understand the bitcoins and till they will own the bitcoins. Than there will be chances that bitcoin can replace dollars. Bitcoin has strong potential but it needs and depends on Internet. Without the access of Internet, bitcoin can be used, stored .
I agree with you people need to have knowledge before bitcoin can replace dollar but i think there are more possibilities than replacing dollar i think it will replace paypal because it is better to use and it is also has an online exchanging method.