Maybe not yet practical. I would guess the R1 chip, which handles the input from all the cameras and other sensors, needs to be on the device. It would be mostly useless on current iPhones, though future iPhones might be more geared toward spatial computing. Having the rest of the processing on the iPhone would introduce more lag, especially if the communication were wireless. You could connect with a wire, but you'd still need the battery (iPhone battery isn't strong enough), so there'd be two heavy dongles hanging off the headset.
Maybe it can be done, but I don't think iPhones running two OSs simultaneously (iOS and VisionOS) is the way to go in the short term.
