It just depends on your definition of mainstream. I personally don't think Bitcoin will ever reach a certain amount of adoption that you can say that it is being used to the full. It's an optional tool for people looking to be and think different. Bitcoin isn't something that non Bitcoiners will be waiting for. They will keep using the traditional payment solutions as it gives them more trust and confidence than Bitcoin. It may sound very harsh, but it's the hard reality. And when people are coming into Bitcoin, then it's just because of them thinking it's easy to gain short term profits.
Ask people in venazuela
Bitcoin will be like the new gold standard when segwit is active , layer 2 systems will be used to expend capasaty.
Bitcoin will be the underleying secure network , the transactions will be done in layer 2
and then the totals per X transactions in 10 minutes will be written in the blockchain.