I don't suppose there's any chance that Siri will come to the iPod Touch after the beta stage...
Nope, no chance at all. As others have mentioned, Apple claims that this is because it requires an A5 chip, but I don't quite believe this since the language processing is passed off to the Apple servers (hence the internet connection required). Mostly, I think it's pretty clear that they see this as the big differentiating feature of the 4S and I'd say there's zero chance of Siri coming to the iPod touch for at least several years. Beyond that, who knows, but I suspect they want to keep it on the new iPhone only for a while.