To be honest, I've never found the need for delegating a huge number of methods in my own work, but then I've never wanted to add a feature or field to something as complex and featureful as e.g. a DataFrame. What issues have you run into when using method-forwarding/delegation macros?

The nice thing about the Julia ecosystem is that people tend to be pretty willing to step back and define their methods in terms of an interface (Tables.jl in this case) which then allows code reuse without brittle delegation. Having to put so much effort into changing the structure of upstream doesn't seem ideal from a composability perspective though.