Bitcoin will be like gold. people will buy it for its value not necessarily for payment methods like fiat. I think the intention of the questions is really "When crypto will be mainstreamed as a payment method".
To speed up Bitcoin adoption, we'll need to start talking about Bitcoin importance and how it can help as a way of long time investment. Many people that ignores any thing or words about crypto may have been brainwashed about the disadvantage of holding Bitcoin like when it comes to volatility, instability and other factors. We need to is increase Bitcoin adoption by educating people about it.