Tom, my impression was just that it was simply offline Photosynth. As far as 4D, we can move through our synths chronologically by sorting by filename. I'd be surprised if Geosynth was offering anything over that. As far as the 3D goes, perhaps there would be a few dials to twirl to utilise greater than 1.5 - 2 megapixel versions of our photos during image feature matching to result in finer results? That's pure conjecture though.
Primarily this looks to me to simply offer privacy for companies who must guarantee absolute privacy of their synth results (i.e. special effects studios, military, contractors, etc.) Possibly there is some documentation distributed along with it that documents the point cloud format for commercial use, but that is again conjecture.
There is also the secondary benefit of not waiting for upload and the fast loading of using Seadragon locally rather than over the net. Other than that, I think you nailed it.