[jmull]

It seems like it could still be coming. They might be following the same pattern for SwiftUI (and Combine) that they used with Swift itself:

1. Create and introduce it as proprietary

2. Iterate fast, changing a lot of things to improve it quickly.

3. Stablize

4. Open source it (and continue iterating with an open process)

The advantage to starting proprietary is the initial iteration phase can move move quickly and stay focused on the goals of the people in the controlling group.