In one of the Build talks about LOB metro apps, they indicated that we should have no problem porting 98% of our apps to store apps, but that the 2% remaining could stay on the desktop as "legacy". That seems out of touch with reality.
The store version of Microsoft apps I've seen are all simplistic reductions to their desktop counterparts. Look at Messenger and Lync as examples. I would like to see examples from Microsoft of complex apps working with the Modern UI.