My personal guess is that S9 will not be released before halving, so that BITMAIN can adapt their pricing according to the trading and mining market reaction. If there is no surge in BTC price ahead, it will probably be a couple of months before difficulty settles back to equilibrium.
After the halving, S7s could hardly make any profit without free electricity, even with the cheapest rates on the planet.
That is, if the price would not surge upwards. It's a high-risk-high-reward scenario, so expect a lot of sells before the halving season. The Gh market is gonna get flooded with cheap s7 hashes.