Who is advocating for this besides you? Current Apple displays are some of the worst computer displays ever when it comes to fingerprints and grime - they would have to get rid of glass. I have been using an X60 for about five years and have literally used the stylus twice, just to see that it works. My wife is a commercial artist and uses Wacom tablets. If she had wanted a drawable display she would have found some way to trick me into paying for a Cintiq by now. The collaborative thing is a non-market - the last time I used a digital whiteboard was in 2006.

I can see a giant tablet with a desktop stand and keyboard becoming the new PC as a more plausible scenario than the iMac/OS X getting a touch UI.