What are the chances that Bitcoin changes its proof-concept one day? Is it realistic/possible that the bitcoin core team make a new Bitcoin Improvement Proposal (BIP) on day in which they propose to change Proof of Work (POW) with something else (proof of stake for example)?

And yes, I know that POW was already part of "Satoshi Nakamoto's" paper Bitcoin: A Peer-to-Peer Electronic Cash System.

POW takes already more energy than smaller countries and it's proved that there are cheeper solutions (the existence of many alt-coins proves that).

Do you think, it's realistic? Maybe far in the future? Maybe without a hardfork?
Chances of a replacement are very low. In fact, this is actually mentioned in the bitcoin community maintained wiki, which seems quite official.

See the "Prohibited Changes" list, where adding an alternative proof algorithm is listed under the "disputed" category. 


  Disputed:
  Adding alternatives to Proof of Work such as Proof of Stake. This could change core bitcoin too much, but with widespread agreement of some sort might be possible.


Note that they talk of adding, not replacing.