> It’d probably be some new PKI on top of SSH where your private key would be held in escrow by an identity provider.

There's only a small problem here: the SSH private key is not used to encrypt the connection. It's used solely to authenticate the connection. The key used to actually encrypt and authenticate the data is an ephemeral key derived through a Diffie-Hellman key exchange during the connection establishment. That is, having the SSH private key does not allow one to decrypt the data after the fact. The only thing having the SSH private key allows is doing a MITM attack, and since SSH does mutual authentication, the attacker would need to have the private key for both ends of the connection.