@KTRosenberg Eye tracking in mixed and immersive space is supported in the sense that looking at a thing and tapping it can trigger a gesture, but any information about the interaction or the "gaze" is entirely abstracted away. For example on macOS/iPadOS in SwiftUI, you can use onHover(perform:) to trigger a closure when the users mouse enters a View, however there is no way to do this on visionOS, as Apple does not inform you of the gesture until the user taps to confirm the hit.
Apple are of course aware of where you are looking as they use the information to do automatic hover state on views in SwiftUI, or to update the state of any Entity that has a HoverEffectComponent, but if you either want to do drawing outside of RealityKit (in which case the HoverEffectComponent will not be available, and gaze information in general is unavailable), or you want to do custom hover drawing in either SwiftUI or RealityKit, you are stuck.
It's understandable why this approach has been taken if Apple are protective of gaze information for privacy concerns. If you has the ability to know when a view is hovered, there's many ways you could abuse that to determine where the user is looking. Apple clearly feels this would be abused, likely by advertisers and bad actors.
Of course... I can't help but feel that if Apple had a way to inject custom drawing into RealityKit (not just pre-canned Entities, or products of RealityComposer), this would be lessoned. For example, it would be nice to be able to stream geometry updates to a ModelEntity, without having to rebuild MeshResource - if you could have some way of indicating that the shape (for example) has changed, and it would request a new position buffer only. But even with that, RealityKit still has a long way to go to fill the gaps that force you to use Metal, including proper geometry hit testing against the surface of the mesh, and true custom shaders that allow me to describe a custom BRDF or custom effects, instead of the not-that-helpful CustomMaterial. But I guess this is a v1. 🤷