Not sure about the trailer assist issue, but I do know that I'm going to rent a trailer and tow an F150 around town with my LR4, just to flex on the 99% of my neighborhood that has a Ford in the drivewayNothing visual to showoff, but some real impressive towing capacity. The rig is around 7,000 pounds (~2200 Uhaul autotrasporter and ~4800 lbs Supercrew F-150). This trailer is definitely too small for Supercrew (I knew that), but doable (made it 120 mi). Used ramp boards as "extension" and locked them in place (so they don't slide out on a highway) with some large bolts and nuts.
Hitch weight scales showed ~400 lbs tongue weight, which was definitely too small, and I really felt that on a highway (some very apparent trailer sway >55mph, another good reason to stay within uhaul recommended 55mph).
It's annoying that LR4 doesn't recognise that the trailer is attached when trailer has LED lights. I've even attached a 10 Ohm (50W rated) resistor in parallel between white (grond) and brown (tail/running lights) wires, but that didn't help either. I suspect all 3 wires should have resistors connected in order for LR4 to recognise that the trailer is attached.
I wonder if trailer sway control is active only when LR4 sees that the trailer is attached? Because I didn't feel any help from LR4 in controling the sway.