beat detection and APE
If the beat could be changed via APE plugins, I believe it would allow the creation of a much better beat detection systems, even customizible by the visualization maker (to help with an individual AVS) AND user (to help with an individual song).

I imagine unconed would come out with a spetacular plugin that allowed a person to choose what part of the band (like in the getspec function) winamp should use to detect the beat, or even something like an option for auto-predict beat only if above a certain percent of "confidence" would also be very helpful.

In any case, if the programmers of AVS allowed this, they could leave it up to the APE programmers to make the improved detection systems.