What will people call it when coders rely on vibes even more than vibe coding?

Writing specs

Exactly my thought. This is just natural language as a specification language.

...as an ambiguous and inadequately-specified specification language.

In the end, every specification is specified via natural language, this is just where the buck stops. All math books are written in natural language, even the ones about specification languages.

Huh? Is ABNF a "natural language"? Is the Go language spec a "natural language"?

How is ABNF itself specified? Yes, via natural language. And the Go language spec is written in natural language, too, you can check for yourself: https://go.dev/ref/spec

ABNF itself is specified with a well-defined grammar and syntax...

Yes, but the spec is still done in natural language: https://www.rfc-editor.org/rfc/rfc5234

Just like any other RFC.

Haruspicy?