It depends on the person. If you ask when the majority of people will feel confortable using BTC I think it would be after a very long time, surely not in our life time, maybe never.
The vast majority of people don't understand money, how they came to be and what they represent... how do you aspect them to understand the benefits of using BTC as a currency?
I think it is matter of time. Take a credit card as example. The Charga-Plate, developed in 1928, was an early predecessor to the credit card and used in the U.S. from the 1930s to the late 1950s. Until 1958, no one had a stable revolving credit financial system by a third-party bank; that was generally accepted by a large number of merchants, as opposed to merchant-issued revolving cards accepted by only a few merchants. Only in 1958, Bank of America launched the BankAmericard in Fresno, California and became the first successful recognizably modern credit card. So, it took 30 years...The vast majority of people don't understand money, how they came to be and what they represent... how do you aspect them to understand the benefits of using BTC as a currency?
You are confuseing things. A credit card is not a new currency, it just provide the means to spend existing currency: the dollar. This is a different thing, I different ideology that many of my friends have a hard time understanding. Make an experiment: try to explain to a poor uneducated man what bitcoin is and you might be amaized of what he understand.
Indeed you are right, but the bigger the change the bigger the resistance, and BTC over usd it is a huuuuuge change.
And this is a beauty of bitcoin. 
