I think there are far better ways to get more interior room than to increase the size of the car (for example - moving the rear seats back into the boot further but having a flat-folding rear seat for when you need to carry larger things).... The last Altezza/IS weighed very little compared to the current one... I would LOVE to see the IS go back to something maybe a little heavier than the Altezza, but keep the same V8 as an engine
I know the current gen IS is a sporty car already, but I really think losing a bit of weight on it would really transform the whole car...