They HAVE to talk about the following:
-Wii sales
-DSi sales
-WM+
-WM+ 3RD party support
-Wii Sports Resort
-Wii Fit +
-Zelda: Spirit Tracks
-PokeMon Soul Silver & Heart Gold
-some other big holiday title(s)
It really depends on how much time they're going to give the above, but there's plenty of other stuff (that we know about) they can show off or highlight from 3RD parties as well...even if just in montage form (though I think some will have their own presentations to be honest):
-RE
SC
-TvC
-MH Tri
-DQ IX & X
-FF:CB
-FF4:TAY
-Dead Space Extraction
-The Conduit
-Red Steal 2
-TMNT
-Silnt Hill
-A Boy & His Blob
-Cursed Mountain
-JU-ON
-Mario & Sonic Winter Olympics
-NMH2
Granted, that's all stuff we already know, we want something new...and we know it's out there from Nintendo and 3RD parties and I think some new stuff will have a big chance of being announced/shown at the pre-show conference:
-Nintendo video service Channel for the west
-DSi Virtual GameBoy/Handheld service
-new Virtual Console Arcade classics
-some kind of WFC "fix" like they offered the SD card fix
-other new Channel's or services
-Bethesda's Wii title
-Retro's next project (Kid Icarus?)
-Factor 5's Wii title
-something else from CAPCOM
-maybe Disaster coming to the USA
-High Voltage's next project(s)
-Pikmin 3
-Modern Warfare 2 on Wii
-something else top secret we don't know about
Potentially, Nintendo has the cards to play, it's just a matter of how/if/when they will. We know that WM+ will be one of their big pushes, but what better way to push it then by revealing a new Zelda title that supports it? I mean, we don't know, but even if half of the above points are revealed, I think it'll be a good show with or without Zelda. And have you considered some crazy scenerio like:
-Wii price drop
-new Wii colors
-WM+ Wii bundle
-Wii's future
-Wii GTA
-Wii Kingdom Hearts
-F-ZERO
-Kid Icarus
-Star Fox
-Pilotwings
-next Mario
-RE5 and/or SF IV on Wii
There's already been big stuff reveled or hinted at for Nintendo leading up to E3, so it's not unlikely that there will be big (or even bigger) stuff at E3.