I'm going to quote Jorge from the Winstep Forums on a similar topic involving the Nexus dock. Same should apply here.
"Microsoft's integration of RT/Metro/Universal/Windows Apps (whatever you want to call that abomination) such as the Edge browser into the Win32 desktop world is pretty much half-baked (although it's already MUCH better than what it was in Windows 8.x).
Metro apps do not really exist in the Win32 world, they run on a separate universe, a different OS inside classic Windows. With Windows 10 MS made an effort to wrap Metro apps inside a thin Win32 'shell' (for instance, Metro apps run inside a Win32 'container' window) but even that is half-baked, which is why you get a generic 'box' icon to represent Metro apps if you have the dock set to show running applications.
You see, Metro apps don't even have what you could call an icon, and MS made absolutely *no effort* to allow 3rd parties to get an iconic representation of a Metro app.
There is also no 'executable' that can be browsed to and/or used to launch a specific Metro app"
Original text can be viewed here:
http://forums.winstep.net/phpBB2/viewtopic.php?f=2&t=9652&start=0
About 2/3 down the page.
