They had to drop M4A support due to legal reasons, but they added audio plugins, which should make it possible to add support for any kind of audio format via a plugin. So there will be an M4A plugin that one might need to compile yourself (though on OSX that shouldnt be too hard).
They also recently held a developer meeting to plan the future roadmap:
Not mentioned there, but beat juggeling and beat detection improvements are already being implemented into Mixxx by a developer:
Not yet clear though which version will get this feature, but the developer is hoping it will make it into 1.9.
there is no final plane for 1.9 yet. or rather the recent meeting resulted in the decision to make smaller but more frequent releases, which means a lot of stuff that had been considered for 1.9 might not make it in. but the good news is that 1.9 and following releases will come sooner this way.
