Nintendo will probably just bring the same tech demos if Wii U is present at PAX.
Any Wii U demonstrations at PAX East would be interesting, as that would be the first time the system is available to the public. When I come to think about it, the roadmap of Wii U news is rather similar to that of Nintendo Revolution/Wii:
Nintendo Revolution/Wii
GDC 2005: Mr. Iwata gives a keynote and talks a bit about Nintendo Revolution, announcing hardware partners and some Wi-fi details.
E3 2005: Nintendo Revolution is unveiled. Not much is revealed apart from the Virtual Console and that the controller will be very special, and also that when you turn on Revolution and see the graphics, you will say, "Wow".
Tokyo Game Show 2005: The remote controller for Nintendo Revolution is unveiled, eight demos available.
May 2006: The first Wii game, Red Steel, is shown in the May issue of Game Informer.
Wii U
April 25th, 2011: Following heavy rumors about Project Café, Nintendo issues a press release stating that a new system will be released in 2012, and that a playable model will be shown at E3 2011:
http://www.nintendo.co.jp/ir/pdf/2011/110425_4e.pdf
E3 2011: Wii U is unveiled, people are confused and hilarity ensues when people think footage of Xbox 360/PlayStation 3 games looks worse than something for the same systems.
CES 2012: Wii U is demonstrated, the Panorama demo is available. Reggie gives some interviews.
For Wii U we've been given some details through IR events as well and now we are digging through the heaps of developer comments that have stirred up the pot really, but I don't remember the radio silence being this severe between TGS 2005 and E3 2006.
Where PAX East will most likely fail to provide anything new, the IR event on the 26th of April will surely succeed. And maybe some kind of reveal will take place in the next issue of Game Informer/Edge etc., as suggested previously in this thread.