The 'production' system (2013 Mac Pro) can and should wait at least a few weeks as a precaution, but I’ve installed macOS Sierra GM (Golden Master) on the late 2015 iMac 5K using an in-place upgrade. There was only glitch: the install hung and the iMac had to be forcibly powered off. Installation resumed and was successful, though taking quite a very long time as usual.
The usual issues crop up: Apple removes certain software such as the version of Java required for Adobe DreamWeaver to work, which requires reinstalling the legacy Java package.
diglloydTools works fine, with no obvious issues. My daily tools including Photoshop, TextWrangler, RawDigger, Safair and so on all seem to be OK.
Apple Mail has some issues, just as in El Capitan and Yosemite, speaking to the continuing incompetence by the programmers working on Apple Mail:
- As usual, Apple requires non-reversible “updating” of stored mail. A not so nice move by Apple (every release!), since there is no going back.
- Certain Apple Mail preferences get whacked, including ones useful for security, so re-check mail preferences. This Apple coding choice violates good mail hygiene in a security sense (e.g. enabling loading of remote content in messages, removal of the display of custom mail headers, etc).
- The password for certain mail accounts get removed, and they must be re-done (this happened in El Capitan also).
- VIP senders and other features not yet tested (it was broken in the past two OS X releases).