Touch screen? Yuck.
The future isn't in touching your computer screen, it's in using 3d gestures to control it. See LeapMotion.com, or what some folks are doing with Kinects.
You're not gonna wanna be so close to the monitor as to touch it, and with gestures you can get a big old HDTV (AppleHDTV??) and manipulate the computer screen from afar, even with digits coated with Cheetoh's residue. Typing is still an issue though...we'll see how that integrates.
And since nobody really wants to be in just the plain old desktop computer business anymore, especially Apple, why not just make a big TV into a computer, rather than just a computer monitor? Imagine your 52" HDTV with the guts of a computer squashed into the back, some storage space, and connectors, controlled by gestures...including a virtual keyboard on the screen. That's the future of iMacs IMHO.
Rob