While the collision filtering stuff was under code review, I discovered a major flaw in the way that they were implemented. I had tried to mix them in with the collision masks and groups that Blender was already using, but for them to be usable, you need complete control of the groups and masks. The way it is now happens to work with dynamic and static objects, because I essentially override those in the filtering that was already done. But it can’t be expanded to to say sensor objects without ignoring Blender’s existing sensor filtering, and I don’t know what the ramifications of something like that would be.
In short, I am looking for a better way to implement user controllable collision filtering. Because of this, there is a strong chance collision filtering will not be in 2.64. I don’t know yet how long it might take to find a better solution, or when I will have the time to implement it.