It seems miners not much concerned about short-term Bitcoin price and continue hashing as usual. Bit weird as there must be a lot of S5 and older unprofitable hardware (I guess phil estimated about 500 ph) unless you pay nothing or like 1-2 cents from nearby power plant. Hard to believe last week hashrate drop included disconnecting all of the older and unprofitable equipment and the spike we see last few days is the new bitmain in house S9s (or privately sold to some big mining farm).
I'm not surprised the hash rate continues to climb as S9 type miners trickle out. If S9 type systems were available to the public tens of thousands would be sold. The last batch of 999 sold out in hours.
Each S9 has the hash rate of at least 10 S5s.
Currently the S9 is profitable to power up even if you pay 20 cents per kWh. If you have cheap electricity the profit margin is huge.
It is quite possible the network hash rate will come close to doubling by the end of the year. The limit is the availability of 14/16 nm miners.
I would expect the difficulty increase this period to be at least 5% and probably close to 10%.