I wouldn't get my hopes up just yet. What's scheduled for Thursday is one of Nintendo's monthly retailer briefing in Japan, which they have every month. Last month they had one and that's when they announced the release date for Sin and Punishment 2 in Japan. I'd imagine that during this one they'll announce the release date for New Super Mario Bros Wii since they haven't given that game a release date in Japan yet.
Now the previous October conferences were pretty much one of these retail briefings as well, so it's possible that we will get big megatons this year as well. Of course in the previous years they also had an event planned the same day in America in which they invited members of the gaming media to attend. This year there is no such event taking place in America which makes me wonder if what's going on in Japan might not be that big this year.
So it's important not to get too excited or else your hype train could easily crash.