Steem the way it is now, can not go mainstream for various reasons not just the difficulty of account creation. But the account creation problem will be somewhat halved in the next hard fork which is hard fork 20.
In that network update, Steem will restructure the account creation system. A new function called "discounted account creation" will allow Steem to onboard a lot more users than its current rate.
Steem will also add a new system of resource credits which will be used to allocate network resources to new Steem accounts.
You can read more about this feature in Steemit's official blog: https://steemit.com/hf20/@steemitblog/velocity-hardfork-account-creation-guidelines