Brian, I am no expert on trailer hitches or towing and I know I don't know the answers to many questions. Your comment that air suspension systems work fine with WDH has be going in circles. The air suspension system on some cars adjusts to keep the car level and the height of the vehicle from the road automatically changes with speed. The air system can also change depending on driving mode selected.
I can understand how the bars might be able to be installed if they use chain to make-up the bar to the trailer but the bars that ride on a preset ledge on the trailer tongue might be too difficult to bend to get onto the ledge. The car will stay level while trying to bend the bar. I don't think that the air suspension can be turned off on these cars. Maybe by pulling a fuse or something but I'm not sure about that.
Also, the car can change height for different road conditions and speed. I think this change is less than a couple inches but it could change the driving dynamics while driving. In reality maybe this change in driving dynamics is nothing more than is encountered when going over bumps or dips in the road with regular suspension.
The dynamics would be different on air assist systems that augment spring suspension. I don't go in circles when thinking about using WDH with these types of systems.