As a PEP editor I haven’t found the current scheme problematic. I don’t particularly care how PEP authors break their lines as long as the rendered output looks good and the source text is reasonably easy to read. A formalized line breaking style may make it harder for people to write PEPs and doesn’t offer much benefit.
I’d like instead to relax the current guidelines in PEP 1:
You must adhere to the Emacs convention of adding two spaces at the
end of every sentence. You should fill your paragraphs to column 70,
but under no circumstances should your lines extend past column 79.
If your code samples spill over column 79, you should rewrite them.
We can just say “Lines should usually not extend past column 79” and leave the rest to the judgment of the author, which is what we’re doing in practice. Recent PEPs don’t actually follow the two-space convention; I think we should drop it.