It's not compulsory and so the teams will have to weigh up aesthetics against aerodynamic performance. If there is a performance differential then they will take the option that delivers the results. There is bound to be some way that this adjustment to the regulations can be exploited to some effect.
I haven't seen a picture of the 2014 car yet (if it's on here already my phone can't display it ) but one thing that comes with having a turbo is the fact the cars will no longer need the raised air box. I expect we'll see all sorts of bits around the roll bar designed to feed air onto the rear wing.
I haven't checked out scarbs properly yet... but if CaT is right about the airbox why has scarbs shown it?
Have the FIA dictated they have to be included?
I'd love to see a bit more variation in body styles although wishful thinking in the age of CFD and wind tunnels...
I'm not sure why it's included in the drawing but at a guess I would say he's just used a stock body and is only showing the 2014 nose. There is no mechanical need to use an airbox (take a look at those early 80s turbo cars) because the air is forced into the car via the turbo and the additional pressure from the airbox isn't required. That said, there may be a rule similar to the one that bans the type of roll bar that Mercedes were using a couple of years ago that will see the airbox shape left in place. From a designers point of view though, anything that can clean up the airflow onto the rear wing would be a real bonus and not having the airbox in the way would be a huge help.