I agree this actually makes a lot of sense. The last time the iMac was updated Apple had intel make a special run of mobile processors that were overclocked over their existing chips (the 3.06 GHz version that uses 55W).The really interesting one is the new Xeon L3426. It's a "Lynnfield" core, with Hyperthreading and Turbo (so it would qualify as a "Core i7" on the desktop,) but it only uses 45W max power, as opposed to all the other Lynnfield-derived processors' 95W. Its base clock is "only" 1.86 GHz, but it has an amazing Turbo ratio that lets it boost up to 3.2 GHz. That's even better than the just-released mobile Core i7, which has the 2.0 GHz chip that boosts to 3.2 GHz.
If any Xeon is to go into an iMac, I imagine it would be that one. To top it off, that Xeon is only $284 in quantity, whereas the equivalent mobile i7 (the "Extreme" series which boosts to 3.2 GHz) is a whopping $1000! (And draws 10W more power.) The next i7 down, with a lower base speed, and a lower Turbo speed, is still over $500 (with the same 45W power draw.) So putting this low-power 'desktop' Xeon in just makes sense.
I could see the iMac.
iMac 20" Core 2 Duo
iMac 24" Core 2 Duo
iMac 24" Xeon L3426 1.86 Ghz
iMac 24" Xeon L3426 ~2.2 Ghz