I wonder whether they'll consider bringing it back to smartphones, if/when Servo starts to make inroads into the Firefox for Android codebase. FirefoxOS seemed way too late for any early mover advantage, and too early to present web apps as a credible replacement for native apps (they can replace relatively simple apps but not much further at the moment).
In some ways, it would have been better if Mozilla had just kept it chugging along as a proof of concept, which you could install voluntarily on rooted phones, and use it as a basis for developing the API's, and the parallel layout engine, which along with a few years of development in client-side javascript should improve the reach of web apps. It was in some ways too late, and in some ways too early for the grand launch.