I think that there is probably going to be some kind of touchscreen "iMac" in a future iteration, but I also believe that it is going to be a major design change.
Steve Jobs and his executives just got finished telling everybody in the last meeting that they felt that having a touchscreen in front of your face is not a good answer. Whatever the multitouch device is, it needs to be at the normal rest level of your hands on the desk...not in the air in front of you.
So...I like the technology, and I'm glad they're planning for the future. But I also agree with them that the touch surface needs to be something you can move around like the iPad, or something you can have on your desk like the Magic Trackpad (which is absolutely incredible!).
I can just imagine that at some point in the future we will see a 27" iMac that resembles a console on Star Trek, with a big touch surface that is just slightly inclined up off of the desk for an easy way to look and easy way to operate.
I have faith in them. 🙂