With x-mode, you do have an off-road mode and you can obviously claim locking center differential anyway.
If they restrict vehicle types, do they also help with extraction etc? If they do not do the latter, what justifies the restrictions? I assume it is public land.
As a last resort, maybe a unified Subaru/VW/BMW owners petition might be in order.
All these 4x4, low-range capability assumptions are so last millennium, lol. I would understand for rock crawling, but to deny a Subaru access to sand....