I expect it to be the Z34 chassis upgraded hopefully with as much of their 1.2GPa Steel as possible. The 6speed is hopefully a reengineered carryover and they'll bring in the new 9speed auto from the Titan and Frontier that they are licensing from Daimler-Benz. And lets hope their has been a focus on the unsprung elements as well esp. with regard to vehicle dynamics.
With the weights of both the Z34 and A90s similar as is, as long as that vr30ddt has an lsd, then I see the Z35 having zero issues shading (in the least) the A90. The real question is how much does this base 400 HP Z35 w/lsd cost?
edit - just reminded myself that the VR30ddt only adds 17 lbs of curb weight along with the requisite increase in HP and TQ. The world needs to know what that VR engine feels like with a 6 speed manual from the factory.