It's a really striking graph, I never knew that there was a steady increase over the years when you check the September price. I was curious if this was just a "September phenomenon", so I checked the historical data from coinmarketcap.com (available here: https://coinmarketcap.com/currencies/bitcoin/historical-data/) and took instead the May price. Here are my results:

https://i.imgur.com/iA4FZU5.png
As you can see, it shows basically the same trend as your image: Bitcoin price seems to be growing steadily. However, there is another angle worth considering, let's check out the Volume for the same period:

https://i.imgur.com/YG5fhK9.png
So basically bitcoin volume (and hype, media, mainstream awareness, etc.) EXPLODED in the past 2 years. Therefore it's very possible that the last 2 bars of Price data, which really give the "oomph" to the price increase trend, are heavily influenced and/or possibly manipulated as a side-effect of bitcoin exploding in popularity only recently. Either way, thank you for the interesting data and for giving me the idea to investigate from another angle.

Edit: As for the next 12 months, I don't think the mass hype is over, so I think we will likely see a period where the price continues to grow, supporting your initial chart; however, since we had the massive downturn, we will likely also see a remarkable low this year (indeed we had one only a few days ago of $2,400) as the various market forces attempt to determine the real value of Bitcoin without as much hype as last year. In other words, I think we will see a 'high high' and a 'low low' in the same year.