No warning, no support, just fait accompli. Disk Utility RAID volumes work for the time being, but there is no support in Disk Utility for Apple RAID any more.
MPG editorial view: this is not just a technical issue. The way this has been handled is a failure of integrity and judgment (“ethical lapse” might not be too strong a term), notwithstanding the hot air emitted by CEO Tim Cook on respecting users. How can an abrupt ripping out of core functionality in any way be respectful of users?
Such actions generate a deep mistrust of Apple competence and judgment by professional users. Commented upon for years here at MPG with growing unease, this latest fiasco is a logical escalation in line with Apple Core Rot. The steady decline in software quality control in both iOS and OS X is its evil twin. There are no adults in charge of OS X development any more, with iPhone bugs and breaking of critical iOS features on the menu for iOS users. MPG does not consider these things (and many more) as random events, but rather signs of dangerous cracks to Apple’s future.
Mac Performance Guide on the “RAID management”-gate by Apple.