The Get Silverlight page now shows Dec 31 2016 as the end of support for Silverlight in Safari. That seems to be unannounced news and it is unclear if it was set by Apple or Microsoft. The date matches the Firefox end of support for NPAPI.
Q1: Could a Silverlight app continue to be viable (and installable) as an OOB app on the Mac beyond that? Or does the inevitable loss of broswer NPAPI support mean the complete end-of-the-line for Silverlight on Macs? The post here seems to offer some hope, but it is quite old.
Q2: Can anyone point to a source/announcement of that Safari end of support date?
I made a test to see if running an OOB Silverlight application requires a hidden browser process. On Windows and Mac, it appears that no instance of a browser is needed (no iexplore.exe appears in the Windows Task Manager, and no Safari process appears in the list given by "ps aux" on the terminal on Mac OS X).
Since we know that the installation can be done on Windows without the browser, it should work on that OS even if no browser supports Silverlight (as long as the Silverlight component itself is available to the client users).
The question that remains: can we make an installer for the Mac, so that the browser is not involved at any point in the installation process? There is a procedure to build such an installer but it requires the Silverlight application to run in the browser first, to get the ".app" file.
A possible workaround: an installer can be made while Safari still supports Silverlight. The application included in the installer will become out-of-date as its code evolves but since the installed OOB application has a build-in mecanism to update itself from the server, the latest version will be available when running it the second time. Maybe that could save us?