Never one to give bland and non-detailed advice or comments, allow this Texas boy to get his two cents worth. Please? Thanks!
I've never been prejudiced against SUVs in GT... only as long as we're not forced to use a Hummer. One of my surprise vehicles in GT4 was the Toyota Tacoma X-Runner. Don't let its truck image fool you- that is a car that thinks it's a truck. Tuned right, it can spank some mid and high-end Japanese sports cars. Some may say that the Subaru Forester was the first road-going SUV in the GT series back in Gran Turismo 2. As long as there is off-road racing, I welcome the prospect of SUVs. I welcome pickup trucks and the SUVs. If you're talking about SUVs, the extreme would be Dakar "cars." What are known as "Cars" in Dakar are usually SUVs except for some of the cars custom-made for Dakar. "Enthusia Professional Racing" has quite a few Multipurpose machines in the game like the Toyota Land Cruiser, Chevrolet Astro, Nissan Elgrand (the only RWD Multipurpose machine), and even the Volkswagen Touareg. I'd even welcome the Porsche Cayenne if Porsche was included in GT5 (another topic for another time!).
Most of Gran Turismo is centered around road racing with (usually) sports cars and GT and prototype race cars. So the issue of any SUVs sharing the same race track with one another would beg, "why the holy hell are we racing these top-heavy gas-guzzlers?" I think a real auto and racing enthusiast would say that any vehicle can be a true performer no matter how it looks or what it is. Many of these vehicles simply aren't designed for the rigorous kind of racing in GT. Just because it isn't meant to be raced doesn't mean you still can't make it a racer. You're not going to win the Grand Valley 300K in an SUV, but you can build up an SUV to perform the same as or better than even the best of sports cars.
What would I not mind seeing in GT5? Most of the crossover-utility vehicles would be a plus. I've always loved the Lexus RX series, even the RX400h. It's the only SUV I'd ever want because of its beautiful style and just the fact that it's not really meant to be a hardcore off-roader. I'd want one because it can basically be my family and grocery hauler without overkill in getting an SUV. There was even a Lexus RX-series SUV that ran the 24 Hours at the Nürburgring that I've seen on TV once. * The Mazda CX-7 and CX-9 would be two more great car-like choices to hit the road with in GT5. Some of you remember the commercials for the CX-9 dubbing these two Mazdas as the "SUV you never saw coming." Zoom-Zoom. * The aforementioned Volkswagen Touareg wouldn't be bad either. After all, they have Dakar experience, showing it can take on the road and the off road. * I probably wouldn't mind the original SUV before SUVs became the do-everything machines they are today- the Jeep Grand Cherokee. You rarely see these raced, but I wouldn't mind getting one of these dusted up at Grand Canyon or Tahiti Maze. * The Mitsubishi Pajero has long been one of the best machines made for racing for the Mitsubishi brand. With a long heritage of rally racing, PD would be fools to not include the Mitsubishi Pajero series. * Suzuki's SUV beasts will likely be included in GT5 as it's tough to top the Escudo Pikes Peak. GT2 had the less-successful Cultus Pikes Peak, but unlike the Escudo, has functional brake lights. * BMW has about three SUVs I wouldn't mind seeing- the X5, the X3, and the X5 Le Mans Concept (unless you think concepts don't count as real cars).
I finally, while it was once marketed as an SUV, I wanted to include this in its own paragraph. The BMW X6 was marketed as an SUV in the past (Sports Activity Coupe), but is now mostly marketed as a car. Love it or loathe it, THIS is my idea of a "big car" unlike most crossover-utility vehicles because of its looks. SUV or big car? It's your call. Still would be great to see in GT5 if the opportunity arose. That's all from me. Keep on truckin'!
(Though lawn tractors would be fun to race 
Eats sports cars for breakfast my arse. My mama's wagon could beat that in a race around a track.
