Makes no sense for Nintendo to be showing off any huge reveals. There's plenty on the horizon for both 3DS and Wii U between now and next E3.
We have Scribblenauts Unlimited, Monster Hunter 3, Lego City Undercover, Pikmin 3 and Game & Wario all on the horizon for Wii U.
Not to mention there's still plenty of room for other third party announcements, weren't there rumours that Square-Enix were planning to release one of their major titles, probably Tomb Raider. If that, along with Aliens: Colonial Marines and a few others are on the way then the Wii U has to me a very strong schedule for the months ahead.
I don't forsee any major announcements till E3 - Nintendo are going to be up against MS and Sony's new consoles and really are going to need their software to show.
If they can pull well into completion versions of the next Mario and Smash Bros' out of the bag, in addition to whatever Monolith and Retro are working on and potentially even a trailer for the next Zelda then they could really show up MS and Sony. Would be silly of Nintendo to show their hand now when there is already plenty on the horizon.