I don't think they will update the hardware, but I have a feeling they will announce some new features for iPhone, a subset of which will be introduced on the touch. (I'm talking a firmware update here).
Basically, I expect that they will announce a few new apps that were buily with the SDK as some examples of what we can expect after it's released a month or so later.
I'm guessing/hoping this will include upgrades to the Mail, Notes, and Calendar apps, which will all become available on the touch (without hacking). They'll add a new game to show of the "power of the SDK", and probably some iPhone specific apps, like a video recorder, voice notes, etc.
Anyways, that's just a guess. They're going to talk about what a huge success the iPhone is, since Jobs likes to gloat when he can, and they're going to need something to announce while he's doing that, and since we know the SDK is coming they'll want to show it off a bit too. The touch will get iPhone scraps, figuratively speaking.
But, no new hardware until late September/October is my other guess. Right after the back to school sales. I'm really curious to see where they go with the touch in terms of hardware. They can/will just add capacity, of course, but I don't know if that's all they'll do. I suppose better battery life, but those are just small expected increases as technology gets better.
Will they add BT? Camera? Or will they just add new software features and lock old touch users out of them artificially?