I wouldn't count on organic growth. Most Steemians are pseudonymous or anonymous and do not want anyone in the walking world to know about their activities on Steem. Why? First of all, I'm betting over 90% of Steemians are not paying income tax on their Steem income. Everyone in their circle of relatives, friends and acquaintances being able to go to Steemworld to look at the entire history of their financial transactions on Steem would be begging for trouble with the IRS or whatever the tax authority is called in their country. Secondly, not many people would necessarily want their spouses or employers to know about earning some extra on the side. So, forget about most people telling people in the walking world about Steem let alone persuading them to join. In most people's opinion, Steem is way good to be true to begin with anyway. Many people think it must be a scam.
I don't think Steem is done for, however, and that there is no chance for growth. I think if Steem is ever going to have millions of users, those users will be completely cut off from the reward pool and be posting through guest accounts or only having a wallet address (a lite account) at their disposal. They will be players of games like Splinterlands and paying for it. Producing content will always be done by a very small number of people. They will be professionals earning big rewards. Those of us who have been lucky enough to have participated in the beta phase of Steem as bloggers earning dollars on blog posts about our cat or something like that will be able to make money by renting out our Resource Credits to apps that have large numbers of paying customers.
RE: Open Letter to all Steemians - Hardfork 21: Culture Change