Basically your argument is, "Bitcoin may not incentivize improvements in energy efficiency, so we should scrap Bitcoin and use something more efficient." Great, let's do it. The technology is already here, in fact, the technology was always there. Have a consortium of banks operate a distributed public ledger. The banks will charge fees to include transactions on the ledger, just like miners charge fees now, and the economic incentives to raise or lower fees will be similar -- but the fees will be lower because the consortium members will not need to cover the electricity cost of mining, only the cost of operating their servers.

The only problem Bitcoin mining solves is the lack of identification among the miners (i.e. the "Sybil attack" problem). Seems pretty obvious to solve the problem by introducing identity, particularly given that the large miners / mining pools are not really anonymous. Sacrifice the small miners who contribute little to the system, set up a consortium, and enjoy whatever benefits the distributed ledger provide without the waste.

(Yes I know, banks are evil, how dare anyone suggest that we acknowledge any authorities in a system, why should we trust the banks, etc.)