The question is how much it costs to maintain the hash rate, which ultimately counts towards the cost of maintaining the blockchain network. For an efficient blockchain network, this cost should be reduced as much as possible.
I believe that continuous research and development are being done to produce efficient hardware. Having this kind of technology, it would decrease the power consumption hence lessening the cost of operation for maintaining the hash rate. This is one way that I could think of to reduce the energy consumption of devices. Adding renewable energy resources could help as well.
Are there hybrid talks with PoW with PoS already? I'm not sure if I have read some resources about this. I'm thinking about it with like the approach to gasoline cars or something. A hybrid.