It's possible for Steemit to be the reserve currency only if it somehow manages to overtake Bitcoin as the number one traded cryptocurrency with the userbase that facebook enjoyed.Limiting supply in my opinion would not be healthy for the platform long-term as people with the highest amount of steemit could crash it if they ever sold off a majority of their holdings much like the domino effect bitcoin is having from the sale of bitcoin by Mt Gox to pay off it's investors.
RE: Can STEEM ever become a reserve currency?