I doubt it ever will become mainstream, but one path to "mainstream" is when merchants, banks, companies, and payment providers just accept Bitcoin rather than:
1) Pretend to accept bitcoin 2) Pay a sub-par service with high fees to convert any received BTC into USD immediately 3) Encourage customers that don't already hold BTC to pay in BTC, adding another conversion step from USD -> BTC
If 90% of the people I give money to just accept Bitcoin as payment, then it makes sense for me to have a "Bitcoin account", as payment fees could be lower.