I recall doing some homework on this WD hitch topic while researching towing limits on my VW Golf Alltrack (awd unibody mk7 platform wagon-similar size and power to Subaru Outback).
The consensus in 2015-6 was "no WD hitches on a unibody" because of the loads. You need a Body of Frame (BOF) vehicle."
I solved my typical VW long-roof saggy-butt problem by AirLift helper bags in rear, which worked ok.
Then replaced those with stiffer springs and upgraded shocks, with more damping, which is much better.
I had to wait for Bilstein (as an example when the aftermarket) to get around to meeting consumer interest/demand for same on the mk7 platform. And swapped in springs from the Tiguan.
One might be able to further raise ride height in any vehicle with a spacer in rear shock mount, so your headlights arent blinding oncoming drivers/pointing at the moon with severe saggy butt, but careful that you dont overdo it or off tow you are jacked all the time...see pic.
A stiffer rear sway bar is also suggested by some for towing, to help avoid/damp yaw. Concur with Seth; anyone seen this ?
IMHO, as to specific advice: I'd stick with the Passport forum and e-trailer for most relevant platform experience by others who have tried mods, including WD hitches.
Cynic here: Owners manuals seem to be written lately by lawyers for CYA vs actual useful tips on out-of-the-ordinary use.
Case in point: VW stopped putting tow limits in the GolfSportwagon/Alltrack manuals from 2016 on because US regulators about that time required new specs and certifications on all new models for towing,
and IIRC since VW had their hands full with DieselGate, so perhaps the lawyerly decision was to simly leave the specific tow limits blank...even though there are references to towing sprinkled in the manual, and limits specced in 2015 Golf Sportwagon manual.
Ironically, The Alltrack in UK won Tow Vehicle of the Year for 3 years running 2014-17, (but that's the TDI version with German factory tow option with a reinforced hitch and tow limits of 4400#). In AUS the gasser is rated to 2000#, under their country specific regulatory scheme.
And, no I would not assume a gasser would tow as well as a diesel...so I chose the CampInn, vs a T@B or Rpod, for example, as I want plenty of room under "the envelope".
I could bore you with more arcane details, but the point is...
its vehicle and load dependent and where written guidance is lacking, you have to try stuff on, or wait for others, to do so,
based on common sense and comservative adaptation/experimentation with what is available in the aftermarket, or similar vehicles where parts may fit...
just as people have done for decades towing and off-roading using aftermarket parts developed by enthusiasts, or Frankenstein'd-in parts from other similar models.
but now adjusting for unibody construction vs Body on Frame use, and back to how-to: imho: like Sweeney, I'd go "more conservative...on new unibody models".
Hey, Its an American thing, its in our DNA to mod our vehicles- anyone see "Ford vs Ferrari"?
Does the Trailsport version of Passport have sturdier suspension parts? How about the Ridgeline- thats trucklet as a chopped off version of the Passport amiright? Beefier stuff?
I'd stay on the conservative side...of course, that could be to save the vehicle from damage --- OR --- keeping the load on the front wheels where it belongs.