The old input system never provided a good way to use XR controllers to interact with UGUI. (I had to write my own InputModule and EventData object to make this work and it was not a good time.) Is that something that will be made easier with the new system?
Yes. The InputSystemUIInputModule is designed to handle input from XR controllers to allow pointing at and interacting with UI elements. However, XR controller device support is currently being moved out of the input system package (to come back in separate packages, so the XR team can release updates on their own schedule), so you may have to wait a bit longer for a workable setup.
The InputSystemUIInputModule handle XR-UI (pointing) input as well as traditional modes (mouse, keyboard, touchscreen)? Is there an example somewhere on setting it up?