I think them building it in rust is a good thing. But rust is a mozilla project so its not as though theyre doing people favors. What it certainly does is showcase the strength of the language considering they have proven to be so badass
That's sort of what I meant to get at - building Rust is a huge service to other people, and an important one too. Servo is showing that they're really putting the effort into optimizing it and making things work as best as possible.