I'm going to go out on a limb and say that we'll see AMD Radeon HD 7xxxM series GPUs (the gamer laptop PC style GPU boards), 3TB of maximum storage (along with the optional second SSD drive), same 16GB Maximum RAM capacity, and obviously Ivy Bridge desktop-form-factor CPUs, and with that, the corresponding Intel chipset, and with THAT, native USB 3.0 support as Intel had promised would be natively in tow with the chipsets for Ivy Bridge.
In addition, given that the last three designs of iMac have lasted exactly three revs, and given that the rev we're currently on is the third rev of the current design, I'm going to guess than an iMac redesign is forthcoming in this rev. This is going to probably also address the many design and engineering problems with the current design, making a redesign a much more practical option for Apple. Given that this is a redesign, there's a 50% chance that Apple will nix the optical drive from this new iMac as well as a 50% chance that Apple won't, given that the iMac is a mid-higher-end machine and those in the mid-higher-end market tend to be in greater demand of the optical drive than those in the lower-end market, hence why the MacBook Air and the Mac mini can afford to not have one. It is also possible that the optical drive might be a feature solely included in the larger-sized model and would be otherwise absent in the smaller-sized model; a move that would further divide the two iMac sizes into a more consumer-oriented model and a more professional/prosumer-oriented model.
As a Mac fan and two-time iMac owner (in the past), it'd be nice if Apple fixed all of the things that make the iMac a truly annoying proposition.