the cryptocurrency is not only extremely expensive in terms of its mining costs, but also inefficient in its long-run design. However, the efficiency of the Bitcoin system can be significantly improved by optimizing the rate of coin creation and minimizing transaction fees. Another potential improvement is to eliminate inefficient mining activities by changing the consensus protocol altogether. So there is the possibility of replacing PoW by a proof-of-stake (PoS) protocol which can strictly dominate
PoW and even support immediate and final settlement. There are many fundamental issues of a PoS protocol still need to be sorted out and remains much to be learned about the economic potential and the efficient, economic design of blockchain technology.
This is false, it is efficient and secure enough the way it is. Bitcoin is never switching to PoS as your concerns comes from a false premise. Bitcoin mining will become unprofitable, and there will be less and less miners due to its economic development, which is as intended: to slowdown mining overtime.
Coin creation is set in code, regardless of network hashrate. Bitcoin doesn't really care if you spend too much or too little energy to mine it, or if there are millions or a few hundred, it will work fine just the same.
Bitcoin's PoW is proven to work and is here to stay. Furthermore, it is yet to be challenged by any altcoin, PoS or not.