That really isn't that bold. Its already official that Intel are officially launching Yonah the day before the keynote, and its pretty safe to say it will turn up in at least one new product. The most likely contender is the Mac mini, with the PowerBook and iBook also distinct possibilities.
The best info I have though says there will not be a mobile G5.
I'm just hoping that there is something really out of left field and unexpected. I think there are a few things we could reasonably expect: new versions of iLife and/or iWork, some neat updates to existing lines, a sneak preview of MacOSX 10.5, and a lot of chatter about iTunes, iPod and Aperture. All of these would be quite satisfying, though I'd only consider the keynote a hit if we see at least one really unexpected thing that has half the people here moaning about how ugly or stupid it is (before they even see it properly), and the other half jumping for joy and watching attentively for the first of the items to ship.
In the spirit of making a bold prediction though, here is my one:
The Mac mini will be retired and replaced with another entry-level Mac with media centre functionality. It will be physically larger than the mini, will have more capabilities for inputting and outputting audio-visuals than any Mac so far, will have a Front Row remote, and be somehow made at the same price point and RAM/HDD specs as the current mini. ... And the crowd will, of course, go wild.
I also wouldn't be surprised to see Airport Express be reinvented. This has been a great product and customers are only now just starting to work out how good it is, so Apple will of course want to replace it right now with a better one.