Well, LE could offer a proprietary API call to report your status. But, agreed, getting ACME Clients to implement that is a lot to ask. And, for LE carries the same burden of design, develop, doc, and maintain for something that is fairly well explained in the docs already. It would just avoid the need for the (long) process of ACME standard modification.
Oh: I posted before I saw your second update. So, yes, we agree this is impractical 