The submission title has been changed from "Replacing the Jet Engine While Still Flying" to "Mozilla’s project to replace Gecko with Servo" (at the time of this writing). Some of the other comments are pertaining to the "Jet Engine" title. For anybody that might be confused, like I was :)
Does that mean that the original title was bad, as the HN guidelines states, "Otherwise please use the original title, unless it is misleading or linkbait."?
The original title wasn't particularly descriptive. That doesn't mean it was misleading, and actually, I thought it was very apt: they're talking about a technology to swap pieces of Servo in over time, and the jet engine analogy was appropriate (particularly with respect to the complexity). I quite liked it.