Since this event isn't taking place in Japan and E3 is only a few months away, I wouldn't expect Zelda, Kirby, Pikmin 3 or anything that might be popular in Japan to be shown off here. I get the feeling this event will be to announce things that will only have any significant in North America and Europe.
Because of this, I do expect Metroid: Other M to be shown off quite heavily with a new trailer and playable demo. Since the game is scheduled for a Summer release in Japan, it'll probably be out in North America even earlier since every Metroid since the first Prime have been released in North America first. And because Metroid is way more popular in America and Europe, it makes sense to give it a huge conference since 95% of it's sales will come from both of these territories.
And if the rumor about Sonic being in Mario Galaxy 2 is true, then I expect Nintendo to officially announce it here as well. Since Sonic is only popular in North America and Europe, it'd also make sense to hold a big conference in both territories to announce something like this as well. This would also explain why there's no conference in Japan since like the Metroid series, the Japanese don't care about Sonic either and so holding a big conference to announce him wouldn't make sense over there.
Plus I could also see Retro's new game being unveiled here. Considering Retro's history and the people who work there, I'm going to guess Retro's new game is probably an FPS of some kind. If that is indeed the case, it'll be a game that has no appeal in Japan either, making it rather ideal to be shown in a North America/Europe event as well. And since Prime 3 came out in August 07, I'd quite possible Retro's new game could be ready to release in the coming months.