Servo right now is more of a Rust reference project than a serious engine. They use the most up-to-date features of Rust and don't worry about having to rewrite

Servo right now is more of a Rust reference project than a serious engine. They use the most up-to-date features of Rust and don't worry about having to rewrite the code with the next version because they know they're working with a somewhat unstable language spec. The real value of Servo right now isn't really as a browser engine, but instead its value as the largest software project currently written in Rust. When you're creating a programming language, you always want to know what it will be like to build large projects in that language, and that's exactly the experience being gained right now with Servo.