Android only recently released APIs for sound that are accurate enough for these kinds of applications. As the % of devices running Android 5.0 starts increasing, we'll see sound mixing (and similar) apps there too.
While Android's sound APIs before Lollipop did have a very high latency, you could hack around it by doing your audio processing in native code and feeding the APIs PCM. It just sucked.
That said, definitely excited for the new sound APIs. It's been far too long.