Launching a desktop program with metro app?

Microsoft is really moving away from allowing 1 app to launch another app, there are many security vulnerabilities associated with such a technology, the biggest one being the command injection vulnerability. Microsoft's solution to this problem was to use what is known as the launcher, the launcher doesn't directly launch another application itself, as you would in the days of C++ where you would just call system("Your command") or pre metro where you would fire up a diagnostic process. Rather the launcher, which is, a Microsoft technology that's been around for a while directly calls the OS, to launch the application associated with such a file.

Microsoft allows you to associate file extensions with applications, see the context menu & the "open with" option by right clicking on a file. So Microsoft allows you to make that association and it's through that association that Windows, and more specifically windows 8 will determine the best possible application to open that file extension with.

Rather then you calling note pad, to open a text document through the diagnostic processes, you will now call the launcher, with the file you want to open, and the Launcher/OS will determine which application and the safest way to open the application.