I like it - if for no other reason than it highlights capitalization issues, like for Class-specifier above.

More seriously, not being a core expert, I have gone reaching for this kind of tool many times - it would be extremely helpful to find it one day.

Editorial committee consensus: This approach is good. Fix intro text. (Do not remove grammar names from main index.) This makes it easy to see where we screw up. Try to also add index entries for grammar terms used in the definition of other grammar terms.

"Try to also add index entries for grammar terms used in the definition of other grammar terms." is mighty hard, because we just mention other non-terminals inside a bnf environment, without further markup which we could hook with creating index entries.

We could define a short markup such as \nt{blah} inside bnf environments for the non-terminals, but we would still need to manually iterate through all grammar snippets to add the markup. Postponed until #1821 has been resolved.