Wait, what? You want Apple to make the display touch screen so you could pause a movie or switch a music track in iTunes? So you want Apple to add in more technology, which would probably translate to a higher priced Mac just to do simple, trivial tasks as that?
You do know that there are media keys on top of your Apple keyboard for just this sort of functionality, right? I also believe if iTunes is your current app in focus, the spacebar acts as a pause/play key. This is usually the case for most media players as well. There is even wireless freedom if you have the Bluetooth keyboard. Furthermore, for extreme ease of use of media playback functionality, you can do all of this with the Apple remote app for your iPhone or iPad.
Your reasons for a touch screen iMac are just not very well justified and are already well addressed with current means: Either a Apple keyboard or the Apple remote app.
Edit: How could I forget the third option of controlling your media. The Apple remote (hardware aluminum, the one used with the Apple TV.