Creating a custom shape (collider) type

I was wondering what extensions to Unity Physics code would be required to make a custom collider?

For example, my project might require NURBS to achieve smooth, collidable surfaces (these surfaces will be static).

 

The TerrainCollider was the latest one added after all the others. I recommend taking a look at any point in the code where that Collider is specifically called out, perhaps even tweaking the TerrainCollider itself to act as the NURB control mesh and having it returning different contact points for a smooth surface rather than the triangle faces.

 

I would be interested in this as well.