To the best of my knowledge there is no plan to build a plugin for Outlook for Mac.
Just to avoid any false impression of deflection, I am Mac OS X, Linux, BSD Unix and Oracle/Sun Solaris user.
The plugin for Outlook 2010 is unlikely to work smoothly for Outlook 2013 due deep changes introduced:
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Unlike traditional COM Add-ins, apps don’t require that you install or update a DLL on the user’s computer. When a mail app is initialized by the user, the mail app uses the apps for Office JavaScript object model to provide contextual information about the selected message in the Outlook rich client and Outlook Web App. Your app runs on your web server and any changes you make in your web content will be immediately reflected in your app running on an Outlook client.
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Testing on a spare computer or virtual machine would cause no harm to live installations.