Mainstream adoption will only happen when investors no longer have to jump through a series of increasingly challenging hoops before they can actually invest in anything. You need to exchange your fiat for one of the big coins, then move that crypto over to an exchange or buy coins from another source, and then store them in a wallet before reversing the whole process if you ever want to withdraw. The company that comes along and combines all of this, and gets the public to get involved by buying into their platform, will transform everything. I saw an article earlier that said 8% of Americans have invested in crypto so there is still huge scope for greater investment and I don't think we're close to anything bursting just yet.