Bitcoin will never move to Proof of Stake. The reasons for this are obvious. PoS increases centralization as it gives power to a few. Those with the most wealth will be able to take control of the network's consensus. Imagine how Bitcoin would be compromised if it were a PoS coin. Big exchanges like Binance and Coinbase would make use of customers' funds in order to take control of the entire Blockchain network. It would be something similar to the STEEM/HIVE hard fork where exchanges turned to Justin Sun's side, effectively taking out legitimate witnesses (validators) out of the system.

Believe me, PoW (aka Nakamoto Consensus) is and will always be the only decentralized consensus algorithm in the crypto/Blockchain space. Other algorithms may be energy efficient but highly susceptible against external attacks. Bitcoin developers know PoW is the safest, most secure, and reliable consensus algorithm to date. There's basically no need to change the algorithm at this point, since Bitcoin is working like a swiss watch. We may see a future where most (if not all) altcoins turn to PoS, while Bitcoin remains a PoW cryptocurrency. I'm fine with that as long as decentralization and censorship-resistance are prioritized. Just my opinion