Bitcoin has become an increasingly expensive proof-of-concept. Proving that blockchain can be implemented is going to have plenty of practical uses, probably not as revolutionary as its proponents claim.
One possible future for Bitcoin is that other cryptos will prove to have more utility (faster transaction times, better security, lower energy consumption), thereby usurping Bitcoin. Protocols like PoS, Proof of Time and Proof of Space may be its undoing.
But it is, unfortunately, much simpler to reason on PoW security than PoS and other consensus.