It's very pity but author is not able to continue work on this patch, and I would like to raise this flag.
I'd like to add some comments about patches:
traversalValue patch adds arbitrary value assoсiated with branch in SP-GiST tree walk. Unlike to recostructedValue it could be just pointer, it havn't to be a regular pgsql type. Also, it could be used independly from reconstructedValue. This patch is used both following attached patches.
range patch just switchs using reconstructedValue to traversalValue in range opclasses. reconstructedValue was used just because it was an acceptable workaround in case of range type. Range opclase stores a full value in leafs and doesn't need to use reconstructedValue to return tuple in index only scan. See http://www.postgresql.org/message-id/5399.1343512250@sss.pgh.pa.us
q4d patch implements index over boxes using SP-GiST. Basic idea was an observation, range opclass thinks about one-dimensional ranges as 2D points. Following this idea, we can think that 2D box (what is 2 points or 4 numbers) could represent a 4D point. We hoped that this approach will be much more effective than traditional R-Tree in case of many overlaps in box's collection. Performance results are coming shortly.
It appears that the issues raised in this thread have been addressed but the patch still has not gone though a real review.
Anybody out there willing to take a crack at a review? All three patches apply (with whitespace issues).