When you say "efficiency" I assume. you're talking about the amount of electricity needed per block?
If so, then that's an economic detail, not a cryptographic one.
The amount of electricity being used isn't because of the particular cryptographic process chosen for proof-of-work. It's because it is profitable for that much equipment to be running. That's what the difficulty adjustment does. It creates an incentive for the proof-of-work process to use as much electricity as can still be profitable. This is why difficulty (and total hash power running globally) drops when the price drops significantly.
Miners can easily switch pools. They can even do so programmatically within a fraction of a second without any human needing to get involved beyond the initial setup.
Imagine that there are 10 major mining pools each with approximately 10% of the global hashpower (about 10% of the global mining electricity being contributed towards each's efforts).
Right now, people choose their favorite pool and just stick with it. There isn't a huge incentive to switch pools. There's enough competition between pools that the payout a miner is going to get over time is pretty similar regardless of pool chosen, with the biggest difference being in the volatility the miner is willing to accept in payouts in the shorter term.
With the "delegation" system such as you've described. As soon as a pool was no longer in the running for the current block, there would be no reason for any of that pool's miners to continue to run their equipment WITH THAT POOL. However, there would be a HUGE INCENTIVE for those miners to just immediately switch their mining equipment over to the pool that was still in the running for the block. Once the block was completed, they could instantly switch back to their favorite pool and wait for the next delegation (or just stay with the pool they switched to, thereby consolidating all the world's mining power into a single pool).
You wouldn't have a reduction in power used at all. You'd just have a very fast consolidation of power into the largest pool or pools.
I didn't see the talk, and J.-J. Quisquater may or may not be "a very serious cryptographer" as you've stated. However, it seems to me that one of the following is likely true:
- You've misunderstood some of whatever J.-J. Quisquater was trying to say
- J.-J. Quisquater is not very good at economic theory
- I've misunderstood your representation of whatever J.-J. Quisquater was trying to say