Long-term, with const generics, and VG (or a macro that creates a (a, (b, (c, ()))) nesting like the hlist crate), we could maybe replace format_args! and friends.
However, there is one more thing a function can't do: borrowing arguments. Formatting never moves arguments because the format_args! macro generates references to them, which it then creates std::fmt::Argument out of.
