MLS is alive and well, but it is partly a victim of its own success.
At this point there aren’t any major features missing from MLS and the client applications. While there is always room for improvements, by and large MLS has achieved what it set out to do and is working well.
It’s also true that after work on Firefox OS stopped, MLS is no longer an important strategic service for Mozilla, so the available staff working on it got reduced. I continue to work on it as a part time project, but that is focused on the service side, operations and general project management. There hasn’t been anyone working on the standalone Mozilla Stumbler app or the leaderboard service for a couple months now.
We also get most of our data from users using Firefox for Android and opt-ing into the contribution option in the mobile browser. The number of contributors from this are at least a hundred times more than the number of contributors using the standalone Mozilla Stumbler app. So the Mozilla Stumbler app and its leaderboard where always more of a hobby project.
Looking forward I think MLS will continue to exist and be maintained. There are enough people in upper management at Mozilla who like MLS and the general idea of it. But whether or not it will get more attention and focus again is anyone’s guess.