Thanks for the investigation. I looked into it a while back and it turns out this is actually pretty easy to get working. Unfortunately, the team is very booked and I'm not actively working on iSynth right now :( If we resume working on mobile stuff in the future, I'm sure we'll add this feature.
Actually... that was Aseem Kishore, not Daniel, and Aseem's schedule seems overbooked already, so perhaps that's not the direction to pursue, but I still maintain that since he's already done that sort of thing, he'd be someone useful to speak with.
Greg, for what it's worth, Daniel Gasienica over on the Seadragon team pulled off launching Seadragon Mobile from within Seadragon Ajax on http://seadragon.com
so the same thing should be more than possible with Photosynth.
To me, this would bridge an absolutely massive gap in satisfaction, allowing me to open unlisted synths, more quickly move between viewing and commenting, etc. etc. Some way would definitely be needed to drop back out to Safari on the synth's page from within iSynth (moreso than simply going to the author's profile) as well to make the experience sweet, but I believe that it's all possible.
I know that iSynth doesn't have the official blessing and the team most likely doesn't want to have any obligations to make sure that the app continues to work with the site in the future, but maybe Daniel could work something up for the site if no one on your team has the time with you coding up the way to drop back to Safari after viewing a synth.
Nathanael, No idea what the technical challenge of a feature like that would be. I'd imagine it would either be very easy or completely impossible (for the reasons you mentioned). I don't know what the future holds for Photosynth on the iPhone, but I'll certainly keep your suggestion in mind if I continue to develop it.