So a multitouch iMac might not be as far fetched as you might think at first.
I am not so sure. AN iMac with a multi touch input maybe, but not a multi touch iMac.
What I mean is that an iMac is a desk top system. The monitor is vertical at the back... and your keyboard/mouse is within reach in front of you.
To make the screen mutli touch would be a step backward for input ease... no one will want to reach that far back for input, no matter how nice the interface.
I think it is more likely that a multi touch input device will be added, like the mouse referred to elsewhere on this forum. I just think it would be cost prohibitive to have a multi-touch lcd panel (in addition to the regular screen) to replace something as big as a keyboard, no matter how cool that might be.
But I do not doubt that is the direction Apple is headed.