I do have a private ca service running on an internal ec2 instance, but all the AWS workspaces broker checks is if the device cert being passed by the thinclient was signed by one of the two signing certs you've loaded into the service, so the private ca itself still doesn't manage revocation in this case.
I do appreciate the suggestion. My main goal in sharing this use case was to show folks that there are many places certificate are used that let's encrypt isn't geared up to solve. Other examples are things like signing Microsoft API requests, etc.