I just don't see it. Bitcoin could be forked to no longer use PoW if it became an existential threat.
Doing the same for Bitcoin would be very hard, and if it simply follows Ethereum's footsteps, then it is unclear why even use Bitcoin.
But -- I hope we see this fork sooner rather than later. Bitcoin miners will have no economic incentive to capture back the CO2 produced.
Ethereum is built to a spec. That's why the different client developers had to coordinate their work. This is not the case with Bitcoin. There, the official client is the de-facto spec you have to comply with if you develop another client.
The bigger problem is that the current narrative of Bitcoin heavily discourage hard forks.
Transitioning to PoS would be a social task with Bitcoin, not a technical one. Also note that Ethereum was promised from the beginning to transition to PoS, they just didn't expect to take this long.
If the Bitcoin developers would push for a POS hard fork I would expect the chain to split into a POS and POW version but which version would become the canonical Bitcoin would be up for debate.
ETH is still on PoW and will continue to be on PoW for many more years.