It's maybe a bit of a hot-take but notation diversity was quite necessary. It's easy to forget that BNF was largely built for textbooks and white boards and it

It's maybe a bit of a hot-take but notation diversity was quite necessary. It's easy to forget that BNF was largely built for textbooks and white boards and it was designed primarily from the perspective of language generation. While language generation and language parsing are mathematically duals of each other, BNF was always under-specified and under-qualified to use for describing parsers, especially for describing (easily or cheaply) computable parsers. A diaspora of notations was somewhat inevitable, and there was never really a "golden age" of BNF for describing parsing grammars. (Even classic tools like yacc/bison were always custom-extended variants of BNF, and BNF always had to be written with a specific parser model in mind; LL(1) grammars were never immediately compatible or comparable with LALR(1) grammars or LR(1) grammars, etc.) BNF will probably always be a useful communication tool, but it has always been deficient for describing grammar parsing and it certainly will never be useful for grammar comparison like this paper seems to be looking for.