What Jack attempts to do is to provide minimal latency, iirc.
I remember a long thread here on LWN where it was clear that some of the posters had no clue about real-time constraints on audio processing and mixing.
That said, I am puzzled as to what the use-case of Jack on Android is. If all you're doing is playback, you only need consistent latency. And if you're doing audio processing, surely you want a far more powerful system that Android is likely to run on.
That said, "because it's there" seems to be a powerful motivating force :-)