I doubt you'll see USB though. Apple isn't all about that. They make their devices to work how they want them to -- not how you want them to, for better or worse. It would also hurt the form factor, probably, which I'm guessing they're unwilling to compromise.
Since the primary reason to stick a USB port would be "non-computer" device connectivity (cameras, mp3 players, stuff that can charge over USB), they could stick a mini-USB port on the iPad2 without effecting form factor. Even a micro-USB port would be an option, considering that micro-USB charging will be MANDATORY on all cell phones sold in Europe from next year (new models, I'm assuming).