I think Chris is a shoe-in for this program, especially since he was in the last one apparently.
I also think who you invite depends somewhat on what you're going to show them:
If you're going to show Tablet stuff, you need Marc Orchant.
If you're going to show Media Center stuff, get Matt Goyer or maybe Chris Lanier.
If you're going to show Longhorn's search/browse/organization functionality you've already got a good list of people interested in that field.