Technologically there's nothing really bad about them (imagine a managed version of ssh keypairs). Technically they could even be backed by physical devices lik

Technologically there's nothing really bad about them (imagine a managed version of ssh keypairs). Technically they could even be backed by physical devices like Yubikeys and never touch the cloud. My worry is the actual implementation, where platforms might lock you into their cloud as the sole provider simply by not implementing interoperability...