I’d read that more as “A blanket prohibition on deletions would be unworkable in practice, and hence any realistic proposal needs to be focused on limiting and/or advertising deletions rather than disallowing them outright”.
For example, we currently only have yanking (hidden from release listings, artifacts all remain) and hard deletion (release artifacts are immediately removed).
What if we had notions like “pending deletion” or “ephemeral releases” where project maintainers indicate to the index operators that the artifacts can be deleted as necessary for quota management purposes, and this status is made visible in the API so tools can issue warnings when pinning to such releases.