I think the last part here is key to building a proof-of-work based consensus without all the energy consumption.

At some point in the blockchain economy, when the (logarithmic) price curve crosses the corresponding curve for difficulty - possibly with some adjustments because price and difficulty are not 1:1 - it will make no sense to throw additional hashpower to the network.

So when such a situation happens, which I'm guessing will be after a few decades, ASIC vendors can include a "sleep mode" with Wake-on-LAN feature so that a pool can wake up the miner when the difficulty reaches a certain threshold.

My suggestion won't lower existing energy usage, but puts a "soft cap" on the energy use without the need for a soft fork.