I don't see it happening bitcoin will take over the dollar are even a small currency. Which is not bad, since the goal is different.
When it comes to competition of the altcoins, there is no even at 5% when it comes to the infrastrucure.
It will surely replace dollar in 50 years time,at that time the bitcoin will be mainstream and all the country is using bitcoin.
Supporters of bitcoin have been making movements so that bitcoin will also be supported by big companies.