Request for Anisotropic Friction

In Bullet Physics you can do Anisotropic Friction - meaning that friction e.g. is less when you slide forwards, and more when you slide sidewards. That is, friction has both a X and a Y component.

This is very nice if you simulate a skater skating on ice, but also has its application in e.g. mobile robots.

You can simulate/fake an Omni-directional wheel and a Mechanum wheel by using Anisotropic Friction.