It is silly to assume that by such a date we would not have much more efficient ways of powering this technology with the vast amount of money which IS being and WILL be poured into the infrastructure of maintaining this epic ecosystem.
2/10 for effort
Neither one of you saw or understood that
mining efficiency does not matter when calculating the total power consumption of the Bitcoin Network.
Efficiency only affects
total hash rate and
difficulty, not power consumption.
It is a given that mining hardware will become more efficient for the reasons you stated. However, more efficient mining hardware means that for a given amount of power the network will just produce a larger hash rate. When more efficient mining hardware hits the market miners will just buy more of it until they consume the same amount of power as before the more efficent mining hardware was on the market.
The total power consumed by the network is only bounded by the amount of money available in each block to spend on power.