I spent a ton of time in 2022 looking for people adopting USD for game development and came up with nada. It's popular in vfx but nobody in gaming seems to be adopting it in any way I could find. Has that changed since?
USD isn't usable as a last-mile format, so many game engines still use internal formats that facilitate fast edit-time to last-mile format conversion and compression, mainly as a point of pragmatism. There is some slow adoption of USD, but given that the main drivers of the format are from VFX, it's understandable that it will take some time for game devs to embrace USD fully.
RealityKit (iOS & visionOS AR/VR/3D library) makes use of USD. Native apps and games for the Vision Pro will also use USD, alongside their new implementation of Entity Component System (ECS).
Yes, but using .reality files is better for stuff like games in RealityKit. For example it would contain a GPU-ready texture instead of a jpeg (and a lot of other differences), so it's more in-line with how assets are typically loaded in games.
Epic has started the work to implement it into Unreal Engine and various tools have started adopting it as well. All this within the last two years or so