> we can find untold examples

"All birds have eyes" != "All things that have eyes are birds."

My hypothesis is that wherever we speak about "zero" and some quantity, it seems like we can substitute "no", and the pluralization rules we'd use for "no" are being inherited.

In contrast, it sounds like you're going the opposite direction, starting with sentences that contain "no" where we cannot drop-in "zero". For example, "No star in the sky is green" cannot become "Zero star in the sky is green."

There are? A quick search in DDG didn’t find any examples. However I did get multiple examples of “stars” (plural).

While English is defined by use, that doesn’t mean that all forms of slang automatically become grammatically correct.

For example: “no star in the sky” might be common vernacular in some regions but it wouldn’t be appropriate to use in formal writing. It’s also not a phrasing I’ve encountered before.

> we can find untold examples of "No star in the sky."

But the original example was "What if there was no star in the sky?" so your example is irrelevant. The original example sounds weird (to me, a native speaker). But "No star in the sky is a triangle" sounds OK and contains your example phrase.