A heavily optioned D5 tops out around $85k. Why would they make the SVX cheaper than that? More importantly I buy LR and RR products because of their offroad ability, passenger comfort and space not because some of them have big motors. I have owned many different RRSC and RRS-SC and compared to what other Marques are pumping out they fall short in almost every department. Handling, tech, output... etc. In short buying a high performance LR/RR is like trying to play sports in a dress shoe. Sure it can be done but you would probably be better off in a sneaker.
Interesting way of looking at it. I currently have a '15 X5M and I would still say if you wanted a complete package of do it all you should do a RRS SC/SVR simply for having the transfer case and off-road ability. Does the RRS weigh more? Yes. Is it slower all around? Yes. Is it slightly smaller? I believe so. But it does the one thing you called out in your statement which is, it can go off road if you wanted to.
Now all that said the new X5 will have air suspension and while not as sophisticated I am sure plenty of people will say it can do what the RR/RRS can do most days with what it will bring to the table.
However, while the Mercedes GL has air suspension and comes in AMG form, I would much much much rather have the Discovery with the lower weight (GL weighs over 3 tons I believe), the trick sway bars from the RRS so that the Disco when put in the "S" mode is actually doing something and when I put my foot down it MOVES, IE: V8.
The SVX is everything I have always called out to make up the perfect Discovery to do everything well and still haul lots of stuff. Plus, the V8 will put a smile on your face where the tiny V6 (Gas/Diesel) won't.
I do agree on the pricing though as it will start to be in a tough segment. I think if its base is basic without a majority of options and starts any higher than $90k it will be difficult to jump on. I can spec everything I want on a D5 for $75k or less. Comes down to is the engine and sway bars worth $15-20k??