There's nothing moot about electricity prices, you either mine enough BTC to pay them or you don't.
Electricity cost for a KnC jupiter is ~$70/month. Over the useful lifetime of the machine, thats probably <10% of the overall cost.
OTOH, being one month earlier it will yield about ~100% more bitcoins for a given hashrate.
A machine that is 2x more efficient will be able to run for ~ 1 month longer, but that extra month will yield you less than 1 BTC
The network won't keep doubling forever.
You will be in trouble if you keep telling yourself that. There is no reason to believe they won't keep producing equipment. If there are no buyers, they will mine with it themselves. CoinTerra has confirmed this much as their intention if you e-mail them. Whatever they don't sell of the first run of 2PH they will mine with it for themself.
They won't be mining at a loss. I never said network won't keep growing or that hardware vendors won't produce more hardware pleae don't put words into my mouth.
However say difficulty is now 20 billion and even a miner with a KNC device an $0.10 per kWh is break even. Anyone with higher electrical cost of less efficient device would be mining at a loss.
With constant price it is highly unlikely difficulty will double again in a month. Doubling difficulty in a month would mean deploying 147 PH/s of new hardware. Actually it would mean deploying even more than that because some older tech will go offline due to economic.
Who would be deploying more hardware enough to double difficulty even with older less efficient tech going offline? Someone who wants to mine at a loss from day 1? This is different than someone buying a rig today understimating future difficulty growth. We are talking about a scenario where for most miners buying on day 1 with anything worse than 1 J/GH means instantly suffering a loss. Even if the hardware is free you would suffer a loss. Who is going to convert $1 in electricity into $0.50 in BTC?
So I stand by the claim that the network won't keep doubling forever. Please don't read into that statement. It doesn't mean difficulty won't go much much higher, it doesn't mean those with high power costs should mine, it doesn't mean miners can't suffer a loss. It simply means that difficulty won't keep doubling every month forever and thus saying a rig 2x as efficient as KNC will only be profitable for a month longer is incorrect.
Ultimately for a miners to be profitable LONG TERM in the ASIC world isn't much different than being profitable in the GPU world. A miner needs:
a) a competitive price on hardware ($/GH or BTC/GH)
b) an efficient design (J/GH)
c) below average electrical costs ($ per kWh or BTC per kWh)