According to my research, the average sum a person would invest in bitcoins is $1000. Therefore, 4 million new users are needed in addition to the 1 million current ones to reach $7000.
That seems like a lot to ask for the next 7 months. I think chances are some bigger investment funds are going to have a big impact though.
That is only 25.8% monthly growth in userbase. Which happens to coincide with the long-term slope of the price appreciation curve.
With this adoption growth, without the logistic slowing, we would be at 2 billion people in March, 2017.
Metcalf's Law, as charted by Perter_R, would suggest that the user base need only grow at a third of the rate of price growth. His model is that the network value, i.e. the market cap, is proportional to the square of the number of network nodes, e.g. number of investors, number of transactions, or number of Bitcoin addresses. Price growth averaging 10x annually is accordingly supported by 3.2x annual growth of new users, which works out to 13-14% average monthly growth in users.
http://www.bitcoinpulse.com/ as most know has many adoption indicators being tracked.