This is a rough sketch I've put together in my mind of how an 'ACME daemon' might end up looking.
acmetool is designed for batch operation which works well for small use cases but large scale deployments will work better with a daemon. This will probably expose a service via an HTTP API, so that arbitrary parts of a service provider's stack can request certificates.
This API will need to be asynchronous as it may take arbitrarily long for 'acmed'