Directly after the halving, hash rate spiked down, but it quickly ramped back up, then even went to new ATHs. So if hash rate will drop as a result of halving, I'm not sure when we will see lasting effects. It seems that some investors are willing to keep pouring money into mining for the time being.
I also hear that KNC Mining is going to be bought, re-capitalized, etc. Not sure what implications that might have. Bitmain is also releasing a new miner aimed at "home miners" -- another interesting development. Not sure that we'll see the big drop in hash rate that many have been expecting.