I don’t agree with your reframing of this, but in this reframing of it is in the same way 1.0B1 and 1.0b1 can’t “co-exist” (because they are considered the same version).
The spec on arbitrary equality may actually already call this out depending on how you interpret the phrase “semantic information”, if case insensitivity if not “semantic information” then the spec could be already be read to say that it is case insensitive. But as I pointed out before (in a footnote), the unclearness of this phrase makes it difficult to draw any implications.
Unless some specific point is brought up where non-PEP 440 versions vs. PEP 440 versions are distinguishable in the proposed clarification I’m going to stop engaging on the discussion of non-PEP 440 version support, because whether non-PEP 440 versions are supported are not is not actually related to the language clarification I’m asking for.
The prior discussion on Unicode was relevant because technically non-PEP 440 versions could be non-ASCII, and case insensitivity can be ill defined for non-ASCII encodings, whereas PEP 440 versions can only be ASCII.
The proposed language clarification is just as about whether ===1.0a1 vs. ===1.0A1 are considered the same specifier or not.
One of the points of having a living spec vs. a historical PEP document is to allow for language clarifications, especially when the spec is unclear or contradicts the tooling it was based on, for example here is a prior clarification discussion: Are Developmental releases a type of pre-release?