The E91 is a mule initially for the X3 since that picture is about two years old.
Since the initial idea to this project is that the X3 and the proposed X4 would share the same platform , allwheel drive etc.. in a similar decision. the way the X6 and X5 share practically everything underneath.
Which in turn brings down costs in overall development and like what the X5 and X6 share in development the outcome to drive between the two is marked by considerable noticeable differences even though they are brothers underneath. X3 and X4 would follow the same philosophy.
X4 and X3 would also share engines from a xDrive20d to a xDrive35i , X4 could use sDrive in light of the X3 being all-wheel-drive only.
If you subtract the details (And please do) from this picture and concentrate on the outline only, you can see how the sedan direction could work for the
X4 is purely in response to customer demand for a more alternative mid-sized Lifestyle Sport Activity Coupe.
X4 could also arrive with 3dr Coupe model as well.