If the leaked photos are true, than the case is the same, so I would assume the same number of current USB ports. Having Thunderbolt is great, but I’d still add an eSATA card.
I’m not terribly concerned about number of PCI slots. I’m assuming at least one 16x for the video card, and that, at the moment, is the biggest deal for me. Eventually I’ll add a proper monitoring output card and perhaps the Qio interface card, but that’s currently all I need for the foreseeable future.