If you look closely at the signature long and curving XJ-S rear roof pillars on the Supercat, it appears the designers drew inspiration from the 'flying buttress' concept seen on cars like Ford's GT and some McLaren and Ferrari models. This design is claimed to 'channel' airflow between the roof pillar and rear window towards the rear spoiler, to minimise drag and optimise downforce. I expect we'll see more design features like this when the real thing is revealed.