Gbox is a software cam emulator for dreambox machines, just like cccam or newcs/mgcamd (only worse). The gbox developers are not into releasing things openly and public like other cams and mostly its comercial users that use it and force other people to use it to access their share. I would be suprised if there is a full emulation hack for nagra3........
I think you may have some confusion in that gbox now supports N3 cards allowing you to use official cards (and share them etc). Well nothing new there because those of us with Newcs had that support first a very long while back lol, N3 cards are supported with newcs fine.