I am afraid with the level that difficulty is increasing it will be hard for the little guys to really benefit from mining in the future. I have debated on buying S9's now or just wait for the next generation of miners to come out and save my money in the meantime. Id hate to buy 20k worth of S9's and then something new comes out. Looks like the E10 is 18Th/s . Certainly other companies will have to step up to compete with that.
People have been saying this since 2013!!
Seriously though difficulty will follow price in the long run. The reason diff has increased exponentially is quite obviously because coin price has as well. If coin price was still $100 do you think we would have this much hash rate LOL? It's not hard to see that the more profitable mining is the more people want to do it! As it becomes less profitable less people are inclined to mine. If coin price ever stabilized for a long period of time we would hit a soft equilibrium where only those with the lowest of overhead prices would be able to mine profitably. Believe it or not the system was designed as a near zero sum game and is working exactly as intended.
The problem is that this motion of diff following price is really really slow compared to how fast coin price fluctuates. Diff is always trying to play catch up. With such massive volatility in coin price the old slow train diff just can't keep up.
You can't predict what will happen to diff because you can't predict what will happen to coin price. What we do know is that if coin price explodes or trends up for a "long" time that difficulty will move with it... eventually. 2017 saw both, it makes a lot of sense to predict diff is going up. If newer machines are made available it will only go up faster!
What amount would you consider to be a low overhead per S9?