Sorry, can you clarify what you mean by this? The ACME spec (RFC 8555: https://www.rfc-editor.org/rfc/rfc8555.html) fully specified both the HTTP-01 (Section 8.3) and the DNS-01 (Section 8.4) challenges nearly four years ago. The TLS-ALPN-01 challenge was fully specified in RFC 8737 (https://www.rfc-editor.org/rfc/rfc8737) about a year later.

In addition, the new work mentioned in this letter is ARI, or ACME Renewal Info, which is not directly tied to any of the aforementioned renewal methods.