I'll get in on the betting action...
I'm betting it's not an updated reader. With the recent UK launch, the recent firmware update, and the new Target displays for the 505, I just don't think Sony would spend that amount to promote the 505 with something new right on the horizon.
I'm also betting it's not a relaunch/redesign of the bookstore. I'm with vivaldirules...too much fanfare for just a bookstore update.
So what
do I think it is? Maybe a wireless add-on for the 505? Or perhaps an announcement of partnering with major textbook publishers, newspaper publishers, or the like?