The following assumes that the text-only non-canonical format intended consumer is people who like the current format but want to be able to get all the semantic content out of the new canonical format, and that the HTML format will be done in a way where copy-and-paste of text will be easy and predictable.
The text-only format must have the same page height limitations as the current RFC format. It must contain the same headers and footers and page break character as the current RFC format. There is no requirement that the text-only format use widow and orphan control; the use case for this is to allow similar referencing of paragraphs from the text-only format to the canonical format and non-canonical HTML format.
The text-only format must allow for preformatted text and art to be 80 characters wide without wrapping those lines. This is due to the relaxation of the 72-character restriction on preformatted text and art in the new canonical format.
The text-only format must represent all SVG-based artwork as a “see reference” that goes to a stable URL, hosted on the RFC Editor's web site, that is part of the RFC's information page. The use case here is someone who is reading the text-only document with a modern text editor that can follow URLs. For example, if Figure 3 in the canonical version of RFC 7890 is a piece of SVG art, the text-only format would say something like “See http://www.rfc-editor.org/info/rfc7890/figure3.svg for this art”.
The RFC Editor must list all of the changes from the current RFC format to the new text format in a single document that can be used by people who have written text-processing tools.
After the RFC Editor has made the cut-over to the new canonical format (and thus the new non-canonical text-only format), all RFCs with a higher number must be in the new format. This will allow tool makers to have a clear demarcation for knowing which text documents are in the old format, and which are in the new format.