Putting an embargo on the information until E3 would make no sense at all, since at that point...why not just make those announcements at E3 and not bother with the conference whatsoever? If there is such an NDA, I suspect it would only last long enough for the magazine publishers to run their next issue, so they can actually treat it as a "reveal" at the same time as their online journalist counterparts.
As for what this conference might actually contain, I'd be perfectly satisfied with some localization announcements and dates (Picross 3-D, please!). They have plenty of games that aren't out yet in the US that they could talk about, between Metroid, Mario, Reginleiv, Sin and Punishment 2, Last Story, Xenoblade, etc etc, and that's just on the Wii side. If there is a Japanese conference too, we might get graced with a "stealth-release" game that'll come out two months after announcement. They did the same thing with Wario Land two years ago and ExciteBots last year.
So, no megatons, but some nice info and maybe a pleasant (but not earth-shattering) surprise.
