It's not exclusive to Joystiq, I know at least 1up has the info as well, and I'm assuming most of the major news sites and blogs will have it.
Because this seems to be under an NDA until midnight, it certainly seems like it will be something "good" and not more bad news (PS3 pushed until late '07, etc). Paul Gale from 1up said in Kotaku's comment section that "tonight will rock," which further adds to the theory that it's good news. With that in mind, I don't think he would have said it would "rock" unless it were Nintendo news, lest people mock him for daring to suggest something Microsoft or Sony is doing will rock.
FIVE PIECES OF IRRESPONSIBLE, RANDOM SPECULATION...
in order of boring, likely information to way out there nonsense that will not happen but would kick
ing ass:
1. Some surprising feature/aspect of the Wiivolution announced for the first time.
2. Guitar Hero II for 360. We know it's coming EVENTUALLY, maybe now is the time? Devil May Cry or MGS4 are two others that are less likely but still a remote possibility.
3. Price of the Wii announced and/or early Wii release date. I'd think they would save this for their upcoming event, but who knows.
4. One of the three consoles announces backwards compatiblity with the Dreamcast. This long rumored/wished-for fanboy fantasy will never come true, but it always seems to be mentioned at least once. That said, placing this under an NDA wouldn't make much sense.
5. Microsoft has bought Nintendo. The Wii will still be all "Nintendo," but after that they will work together on all future projects, including the Microsoft handheld. Reggie's penis will be grafted onto J Allard's bald head, and he will proceed to beat Kaz Hirai with a Slim Jim until he is DEAD.