Seriously seriously doubt they would do that, maybe someday down the road, but not for the foreseeable future. Gorilla Glass does well in other phones b/c the casings for the most part take way better shock abuse then the glass/metal of the iPhones. Making it stronger to resist scratches, yeh, pretty much all the phones are good at that though now. But completely glass, no way.
Looks like they mention ceramic though too, the SGIII is going to have a ceramic casing, so who knows, could be ceramic/glass combo for the iphones? Guess we'll just have to wait and see.
What would be the point. Glass isn't something I really want to grip, and that's largely the extent of the advantage. An all glass iPhone would still require metal inside as glass is not conductive, and would really just serve as a constant that doesn't add much to the phone itself.