I don't think bitcoin will ever replace the US dollar. The government would not allow that to happen. I could see bitcoin being used as a payment method like paypal, or a method of sending money like western union, or even a way to store money instead of banks.
We are on the same side, bitcoin is nothing compared to dollars. Look at the price now, it's on dollars and that is its standard way of measurement and without dollar bitcoin could not be popular. That's the reality, we are just a small currency and dollar is a powerful currency which reflects its country.