I think the syntactic sugar that you mentioned is not what holding Rust from meteoritic rising. It's its strict constrains like borrowing/ownership and lifetime that could render the existing skills useless for many developers who are familiar with GC or even manual memory management. Many times (or most of the time), Rust compiler won't let you do things that you know it's unsafe but you're certain that it's ok to do and that's because the rule is the rule in the eyes of the compiler. I'm learning Rust and I love the language. It's a brilliant language with a refreshing idea but sadly many things I learned form many other languages cannot apply in Rust. But that's ok :)

About the default arguments, I know some people miss it and some don't. Golang also doesn't support that. There might be something that I don't know, but I don't think it's just a coincident that 2 new languages don't support that. There are a lot of discussions about default arguments in the past and all RFCs got shot down. This note compiles everything for you (I have to go over this myself :)):

https://github.com/samsieber/rubber-duck/blob/master/REVIEW.md