Version 1.8.4.1199 for Mac is now available on the software distribution server (commercial and trial versions). It should work without problems on macOS 10.12 Sierra, and works perfectly on OS X 10.10 and 10.11.
Besides being a new version, slightly more stable and efficient than 1.8.4.1195, build 1199 *requires* to be installed on the standard /Applications folder. Previous versions could be deployed anywhere on the local filesystem. This flexibility is now lost forever since macOS 10.12. Note however, that you can uncompress the distribution .zip file on /Applications and then copy or move the PixInsight.app application bundle anywhere. As long as the original PixInsight distribution folder is on /Applications, the application bundle can now be launched from any arbitrary location.
This is a temporary version to keep PixInsight running on newly installed macOS 10.12 machines. There will be a new release in October with new functionality and improved compatibility with current operating system versions.
Let me know if this version works on new macOS 10.12 installations. Based on your positive feedback, I'll make an official announcement. Thank you for testing.