The Bounding Interval Hierarchy
We implemented a templated version of the BIH as described in C. Wächter and A. Keller: Instant Ray Tracing: The Bounding Interval Hierarchy (pdf) to allow us to insert any kind of Traceable that provides the necessary getCentroid() and getBoundingBox() methods to compare against split planes.
We also extend the BIH by nodes that clip in another way: Instead of intervals from (-infinity,clip] and [clip,infinity) we clip away empty space with the interval of [clip,clip]. We use this when the splitting plane results in an empty list for one of the child nodes anyway.
As this was not one of the features mentioned on the RC sheet, we propose to weight this in the same way as a BVH Structure, for it also is an object partitioning scheme and has quite similar implementation complexity.