In a language like C# or Python you usually want to get an object tree for the AST and you shouldn't have to write any code to get that. It should come "for free" with the grammar.
Another missing capability that people don't know they are missing is the ability to "unparse" the AST back to text. This is valuable when you want to write a code transformer: for instance in query languages like SQL there is a lot of value in doing a transformation on the query and then writing it back to SQL. You should be able to transform the AST and not have to write a line of code to transform it.
Another problem is composability of grammars. If you want to support SQLLite, Microsoft SQL Server and Oracle SQL dialects you should have a base SQL grammar and extended grammars that inherit from the base.
All of these capabilities are so beyond the pale of what parser generator "insiders" are used to that it's a very hard conversation to communicate that these capabilities are both possible and useful.