Servo is an attempt to rebuild the Web browser from the ground up on modern hardware, rethinking old assumptions along the way. This means addressing the causes of security vulnerabilities while designing a platform that can fully utilize the performance of tomorrow’s massively parallel hardware to enable new and richer experiences on the Web. To those ends, Servo is written in Rust, a new, safe systems language developed by Mozilla along with a growing community of enthusiasts.

Written in Rust. No mention of what will happend to Gecko whatsoever in the announcement

Mozilla and Samsung Collaborate on Next Generation Web Browser Engine →
The Servo Parallel Browser Project (GitHub) →