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.
Exactly. Bitcoin will stay as an alternative payment method.
Though it is unpredictable but still i also feel that it may become more of what it is today but it would definitely not be able to replace any currency in the world as it is a free system which cannot be controlled and currencies running anywhere are in control of their governments, so it is really likely to happen.
lack of control is just the most and volnet government of each country. That is why Bitcoin never replace a centralized currency