I think bitcoin will replace dollar but it will not be "soon".
Bitcoin will NEVER replace the dollar. It won't even replace the fiat currency in a weak problematic country somewhere in the world.
The population of bitcoin users isn't enough to make the others migrate from using dollars into using bitcoins. I think it's just a matter of time when people start having an open mind about the digital currency. Bitcoin will be very much popular if people would start having online transactions from another country.
Bitcoin will remain an alternative currency option for people that are open for such a thing, and understand that it can give them the so much loved bit of financial freedom that they have been waiting for. We must be happy with how Bitcoin is right now, because when Bitcoin grows too large, the government will not sit back and watch a potential threat to their economy get bigger and bigger. In that regard, be careful with what you wish for.
The use of bitcoin would become a necessity to the majority of people once they start having transactions globally and not just in their area. But let's face it, not everyone is global minded. Some would just stay as they are for years and won't even bother researching about bitcoins.
If we at some point manage to have 1% of the world population to use Bitcoin in one way or another, then that will be something very special. I don't think we'll ever get to a point where 10% of the world population is using Bitcoin. Especially when you consider that the fiat based payment infrastructure gets better throughout the years, transaction fees of Bitcoin going higher and higher, etc. All things that we have to keep in mind.