Bitcoin is PoW, it is in the whitepaper. However, if everybody agrees, yes bitcoin may switch to PoS as well but I don't think it is going to happen. Some people say PoS is not as safe as PoW and we still don't know if this is right. Eth and cardano doing well so far. So maybe, the hesitations might be baseless.
Bitcoin too is doing fine with PoW, it ensures security and robustness of BTC blockchain. The issue of too much power consumption by bitcoin is as old as hills and IMO its just over hyped. Eth has not switched over to PoS yet as,
Altair, Ethereum 2.0’s first hard fork, is expected to come into effect by the end of the month — the point where the original proof-of-work Ethereum blockchain will transition to Ethereum 2.0’s proof-of-stake consensus mechanism. SourceWhether its PoW or PoS, they both are same way of climbing the same mountain. As PoW is centralized along miners that can afford expensive mining equipment and electricity bills, in PoS those who can stake huge amount of coins will grab the major share of mining.