It will go mainstream when the average Joe starts to care. So far, this hasn't happened, and there's no indicating of things getting any better. Circle so far is Coinbase minus the fees minus API minus adoption minus integrations minus large customers minus mobile apps. The only good thing is the lack of fees and the higher weekly limits ($2,500/week of instant buy vs $1,000), which isn't little, but not something that Coinbase cannot meet and beat given they have a lot more volume and ways to internally settle orders vs heavily relying on Bitstamp.