Please see previous comments [here](https://github.com/JuliaLang/julia/pull/32859#issuecomment-521512416) and [here](https://github.com/JuliaLang/julia/pull/32859#issuecomment-521839355) for the compat/intercept story. In short, there are already ways to overload/provide for custom types to hook in to Printf at various levels. And we're at least providing solutions to all known users/overloaders of current Printf code, in most cases allowing for a much simpler integration.