On iOS Apple switched it to being the default update quietly in a point release: https://arstechnica.com/apple/2017/01/ios-10-3-will-be-apple...

It actually shows marked performance improvements, but that's because it focuses on performance on the type of storage an iPhone uses.

No? Pretty sure with the initial release they specifically said that they were taking their time in testing it thoroughly, but that they wanted some initial feedback from people. It's been in a preview mode available in MacOS for just shy of two years if I remember correctly, but they explicitly said from the beginning that they didn't advise people to use it for their main OS partitions or anything important for a while.

No, it has essentially already shipped with Sierra (only in demo mode for developers), and it's already on route with the final 10.3 iOS version (currently in beta) to become the official iOS FS.

No, it's almost ready. It's already in use in iOS 10.3, and signs point to a full rollout this year.