efficiency of mining keeps increasing, however, difficulty is increasing as well.

In March 2014 antminer S1 was producing 0.08BTC/day while hashing at 178GH/s
In October 2015 antminer S7 is producing 0.04BTC/day while hashing at 4860Gh/s
So, in mere 19 mo, hashing speed of the consumer machine increased ~27-fold.
Efficiency per watt went from 2 to 0.25-an eightfold increase in efficiency.
However, difficulty increased ~54-fold, making the best (so far) machine to produce just half of what it's predecessor did 19 mo ago.

We cannot/do not want to get to $500,000 per BTC any time soon.  Here is the math behind it:

https://bitcointalk.org/index.php?topic=694401.0

If BTC were to go to $500,000 in this era it would cause a catastrophic mining bubble:

   $500,000 x 25 = $12,500,000 per block = $75,000,000 per hour

   $75 million per hour would drive the mining to attempt to use 675 GW.  This is about 30% of all the power generated on the planet.

So, in order to keep our power consumption under about 2% of world wide power production, we cannot/do not want the price to get to $500,000 before era 6, which is about 2033 or so.

Using my previously derived formula for the power consumption:

P = (6(50/2^e) + f)(x)(1 - g)/c [kW]

where:

x = exchange rate [USD/BTC]
e = era [0..32] (we are currently in era 1)
f = average fees per hour [BTC/hour]
c = cost of energy [USD/kWh]
g = average gross profit margin [unitless ratio]

we can look at the power consumption in each era assuming a price of $500,000 per BTC.

In order to make it simple I will make the following assumptions:

x = $500,000 per BTC
f = fees per hour will keep the coinbase above 6 BTC/hour (1 BTC/block) in all eras
c = $0.10 per kWh
g = 0.1 miner gross profit margin