There are a few members happily towing with diesel SUVs, Touareg, and older Liberty and Grand Cherokee. First I've heard of a Q7, but it's very close to the Touareg. They all report great towing experiences with the 400+ lb-ft of torque at 2000rpm with better than any gas engine fuel economy.
However, you really need to check the receiver ratings. I am not aware of any that are rated for more than 740 pounds. 6000 pounds loaded TT is going to be really close, in the 700-800 pound range. The Touareg specifically does not recommend using a weight distributing hitch, but many people do. Do some research on those.
Also, check the payload on all those as you shop. You said luxury, so that means lots of equipment/features/options. That takes away from the already low payload of these mid-sized SUVs. I asked
Touareg owners and only got one response. If you only have 1100 pounds to start, then 700+ pounds of trailer tongue weight, you only have 400 left for family and anything else in the SUV.
Air suspension is common on these luxury SUVs. I don't it for RVing. It complicates weight distribution hitch adjustment and masks overloaded conditions.
What's wrong with a diesel pickup? They will have more seating space than any mid-sized SUV. A $400 bed cover provides quick, easy access to a much larger cargo are, if not climate controlled. You can get a lot of the same luxuries in high end pickups these days.