I disagree. I need a quad-core for video editing and handbrake (both of which do not need Grand Central since they already optimize the extra cores) that doesn't cost over $2000.
The problem is how thin the iMac is. With a little more space, a desktop chip would fit. I do not think this is ever going to happen though, so I am sitting here content with my 2007 iMac, w/ 2.8 Core 2 Extreme. It is still basically on par with the current models, minus the graphics card (but I don't play games anyway).
I don't plan to upgrade until the following:
(1) Quad-Core
(2) LED Screen
(3) SSD Drive
(4) Graphics card with 1gb of VRAM
(5) Firewire 3200
(6) USB 3.0
(7) Blu-Ray
Based on these "desires" I probably won't be upgrading till the end of 2010 / 2011...but you never know.
I am in the same position as you. I would really like to see Quad-Cores in the iMac. I doubt we'll see it this next time around though. I don't think it is a matter of will they but when will they. In order to keep the iMac competitive I'm assuming Apple will make this a reality at some point. Hopefully sooner than later.