I added more details about GiST use cases (PostGIS and ScalaGiST) in my proposal and created one more entry for reviewing other patches in the time table.
I'll try to polish the proposal in the remaining three days to the GSoC deadline. I don't think I have much time to modify PostgreSQL source code and test against it myself though ;(. Many thanks to your feedback.
> 1. The case that the volume of an MBB is 0 should be very rare Nope, if you index data points tend to cluster on grid-alligned planes (which happens with geo data, all points have same height above ocean) if always have zero volume of MBB.
BTW look at PostGIS, they are main GiST users, so indexing their data is important.