In principle, sure, but in practice the main reason people seem excited about Rust isn't as the language in which Servo is implemented; it's as a C++ killer (note, for instance, this article). If it's going to fulfill that role, then being good at writing compilers/runtimes is absolutely essential.
Compilers/runtimes aren't what most C++ code does, surely?
EDIT: People are excited about it because of the promise of memory-safety (fewer crashes and security issues), as a primary driver. Servo is a proof that large-scale programs can be written in this way. They're not just excited about writing things in a new language for the hell of it.
