Some of the previous suggestions look good. Here are some small ones…
The gain/volume separate from the vector movement. Or a way to gain/vol each layer in addition to the vector volume movement. It could even be as simply as having a gain knob in the compressor plugin or a gain fx. Sometimes some samples are a little louder than others and the vector movement makes it a little hard to control the differences of each layer.
For the vector movement, it would be great to have a movement preset thats only two layers. Like layer 1 and 2 only.
Another option would be to have the vector movement only work on the lower two quadrants if layer 3 and 4 are turned off.
Also, playback of samples at half speed, double speed etc.
Small thing also would be to have an option to have categories be just text instead of square icons that look like expansion packs.