Yeah, you can use any type of delimiter with macros, but I think that's an important feature, especially since macros can expand to declarations. Early versions of Rust required parentheses for all macro invocations, and that looked really ugly for anything that looked like a block. Delimiter interchangeability is a feature from Racket that works really well when it comes to macros and I'd hate to give it up.
Agreed. They allow you to naturally create vectors with the bracket delimiter `vec![1, 2, 3]`, create spawn-like macros with the brace delimiter `spawn { code }`, and in the normal case just use parentheses `println!("testing")`
