This is an odd situation and should generally not occur. It seems the VSIX file got copied over but was not installed correctly.
Here's the work around (run using an administrative command prompt):
"C:Program Files (x86)Microsoft Visual Studio 12.0Common7IDEVSIXInstaller.exe" /admin /uninstall:MultiDeviceHybridApps..db151788-9b27-49db-a5e2-d25a2653eb83
This removed the broken entries for the VSIX from the previous failed attempt to install. Following this, issue another command:
"C:Program Files (x86)Microsoft Visual Studio 12.0Common7IDEVSIXInstaller.exe" "%localappdata%MicrosoftMultiDeviceHybridAppsMicrosoft.VisualStudio.MultiDeviceHybridApps.vsix" /admin
At this point, the VSIX should be installed successfully and the templates will become available in Visual Studio.
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