I think playable demos are very likely. Not just tech demos, but demos showing possible launch games. The Wii is coming out THIS YEAR, and the controller as a selling point needs to be experienced hands-on.
At 6 days, 21 hours, and 20some minutes to E3, that could mean that at this very moment next week, I'll have gotten to the front of the line to play the next Super Smash Bros.!
I remember counting down since over a month to E3. Now in mere days a lot of speculation will be over. Depending on what they show, we may be speculating more though. There may be currently unfathomable game experiences that we will all be discussing very soon.