PoS actually refers to "Proof of Stake."
And, no, Bitcoin proper will never implement proof-of-stake: even if it is objectively better.
Bitcoin is a revolutionary experiment. It is the "first secure networked application ever created in the history of computers." (
Out-of-context Bruce Schneier quote) Governments and banks will attack it through legal and technical means. It may only have a small niche over the next 50 years. If that happens, it will be OK: because it is just an experiment.
Replacing "Proof-of-work" with "Proof-of-Stake" would invalidate the experiment. We don't really know if a Decentralized (which is not an easy goal in itself) Proof-of-Stake currency would be a secure as proof-of-work. It is still an open question if the Bitcoin network can withstand state-sponsored attacks. Because it is so revolutionary, states may be reluctant to attack the network due to it's possible strategic importance.