They've done it! AMCE is now a standardized protocol for certificate issuance and management. The IETF has standardized the ACME protocol as RFC 8555.
...Having a standardized protocol for certificate issuance and management is important for two reasons. First, it improves the quality of the software ecosystem because developers can focus on developing great software for a single protocol, instead of having many pieces of less well maintained software for bespoke APIs. Second, a standardized protocol makes switching from one CA to another easier by minimizing technical dependency lock-in...
With this news, Let's Encrypt has also announced that they will remove support for ACMEv1 "soon" as well as unauthenticated get request from their ACMEv2 end-points.