If Passkeys in iCloud Keychain is based on a non-proprietary implementation of public-private key cryptography, I probably would be willing to store login information in the cloud for the first time.
Why? Because if the private key never leaves the device that generated it and if only your public key is stored in the cloud, the system will be more secure than most sign-in methods currently offered.
Company-level breaches, such as what happened at Yahoo, will be more difficult to pull off. Individual level attacks, such as SIM swapping and phishing, won't work. No, it's not perfect security of course–there's no such thing–but let's face it, we gotta move away from SMS, voice calls, emails, "secret" questions+answers, and personal facts from credit reports for authentication. All of those are ridiculously insecure in an age of social media, VOIP, and automated hacking.