Food for thought, have you considered how interactive Mario Kart is probably going to be?
Hell,
@Teebin mentioned in the past that the interactivity levels for the ride beats MiB by a landslide, and that I am more willing to welcome an IP that is classic by it's own right, and not a broken franchise.
As for SLoP, it'll do fine. I would doubt however that attraction taking that much space at this point.
As for SS28, I am curious to see what that turns out in the end. At this point, I am thinking and almost betting that it will be involved in the creation of the relocated Studio Tour plaza.