In the medium term I expect hashing power of the network to continue to decline as there is insufficient real transaction volume to warrant the current network size.
Well, currently mining is subsidized by generation. But once that's over it's not at all obvious that the network hashrate (scaled to hardware advances) will be as high as it is now even if Bitcoin is successful, and the incentives of trillion-dollar entities to attack it become ever greater.
Subsiziding doesn't remove the cost it merely obfuscates it. That cost is felt in inflationary pressure. If the economy only needs 1000 new BTC daily to satisfy growing demand (due to rising economic activity) and achieve stable prices, but instead generates 7200 via mining then the price of BTC relative to fiat will fall. Another way to look at it is 7200 BTC daily reward @ $3 is a ~$20K daily expansion to the money supply. If that expansion is unwarranted then price will fall.
So users of Bitcoin either pay the cost of the network (massively outsized compared to necessity) via direct cost (say a 8% transaction fee looking at volume vs hashing power) or they pay it indirectly via inflationary pressure on their currency.
Subsidy or not the cost is real. At this point there is no economic demand for an 8TH network. Maybe not even enough for a 1 TH network. The current network (at a guesstimate of 2MH/W, $0.10 per kWh and $1 per MH capital cost) consumes nearly $10,000 daily in electrical power and burns through another $1000 in depreciating hardware). That simply isn't sustainable given the tiny amount of economic activity actually occurring.