I think the biggest change would be departure of the high-revving V8 and being replaced by a low-end torque focused twin turbo V6. It will up the game as far as numbers go. I will keep my RCF for that masterpiece engine for its revs/sound/response.
Having driven the RCF for two years and also having read up technical documents, the chassis/suspension is absolutely brilliant for a premium compact sport coupe. Lexus essentially first started with building a convertible chassis by adding all of the reinforcements and braces (in trunk, underbody, doors, door sils, engine compartment) and then welded a roof on top of it. It ended up giving an exceptionally rigid platform. Yaguchi san wanted to remove the roof for a convertible without any added weight penalty (Lexus dropped the idea later on). Lexus initial documents said, it was 40% more rigid than the IS350 F-Sport and 60% more than the GS350.
The extra torsional rigidity is felt everywhere. It gives a very solid and coherent feel to the whole car. Tight turns, high speed stability, angled entry, bumpy roads etc. The downside was of course, all of that extra bracing adds weight, which contributed to much criticized 3950 lbs weight. Also, the sense of speed is masked because of the exceptional stability. On highways, you need to look at the speedo to see how fast you are accelerating. Opening the doors and the weight of the door is felt. I mean, the doors are heavy as hell. Tthe penalty of those big beams running through the sils and door panels becomes apparent.
