Blog article: https://godotengine.org/article/uid-changes-coming-to-godot-4-4/
Discussion about the article: https://github.com/godotengine/godot-proposals/discussions/11574
There's been a fair amount of discussion about this change in Godot github issues and PR's. The above article and discussion were created to explain the new feature and provide a central place to discuss it. The feature was added in Godot 4.4-dev5 (the latest dev snapshot is 4.4-dev7).