Reason why mclaren haven't got a stepped nose is because they didn't keep the chassis high, they lowered it in sacrifice to avoid the stepped nose. This is what Scarbs had to say
Lower nose less space for airflow, but lower CofG, better suspension geo, it could pay off with better laptimes
ScarbsF1 is making some interesting findings. All Ferrari powered cars (Ferrari, Sauber and STR) have tiny cooling ducts. STR have an interesting air scoop under the normal position for the airbox intake. This is for engine cooling, but it's an unusual position. Red bull has a duct in the step on the nose, some say it's for KERS cooling, others say it's an F-duct type device, others say it's to create positive pressure in the cockpit. We shall wait and see. Lotus also have some blank panels on the side of the roll hoop. These panels are believe that they could be future cooling ducts.