I like how Coq describes its grammar (https://coq.inria.fr/refman/language/core/basic.html), though it's definitely not a standard. The Coq grammar and language is very complex with edge cases for niche features so it's good they have a detailed reference (also because other than CPDT and Software Foundations there aren't many references or tutorials out there...).
Even though parser generators are often much different than EBNF, I still wish more people followed this standard, and parser generators could create EBNF grammar definitions. Because it's not just for parsing directly: it's a good starting point for creating parsers; a reference to validate and regression test; and it can be used to generate a (sometimes ambiguous) parser which is good for prototypes and toy languages.
IntelliJ Grammar-Kit also uses sort of EBNF (https://plugins.jetbrains.com/plugin/6606-grammar-kit), the file extension is even `.bnf`.
Even though parser generators are often much different than EBNF, I still wish more people followed this standard, and parser generators could create EBNF grammar definitions. Because it's not just for parsing directly: it's a good starting point for creating parsers; a reference to validate and regression test; and it can be used to generate a (sometimes ambiguous) parser which is good for prototypes and toy languages.