The linked article leaps to conclusions a bit when they say "Dave admitted that Mozilla aspires to replace Gecko with Servo in the future not just in Firefox OS but also in the browser."

The quote from derStandard.at is a little different -- it's in response to a question about Servo from the interviewer, unrelated from the previous talk of B2G (emphasis added):

"I'd say this is less of an experiment than other things we are working on as we have a full team working on this and Rust (the language Servo is built on). And we all have it in the back of our heads that one day we are going to replace Gecko with Servo, but we don't have a specific time frame on it as Servo still so early in the development.