Pretty boring if it's just FFT based. I'd love to see music visualizations make use of more sophisticated musical feature detection, like polyphonic note recognition or tempo/rhythm analysis.
Given the nature of the project, a hackathon, sticking to the last computed FFTs and a notion of time was all we need to play with nice shader effects.
I'm currently playing with tensorflow on my spare time. I'd like to use a neural net to find interesting features of a track and inputting this to a shader. That's what I would do if I had another go at it.