We have reason to suspect that the Zelda team has been working on or at least gathering gameplay ideas for Zelda 3DS prior to Skyward Sword's release. Aonuma's statement of "having 3D in the game will mean something, but you probably won't understand that just yet" late last year also shows that they might have already had a pretty good idea of what they want to do with the game then. Come GDC 2013, they will have been working on Zelda 3DS for at least 1.5 years, so seeing something by then is actually pretty likely. So yeah, I'm expecting a reveal at GDC, or at latest E3 2013.