The Semi-Coanda exhaust system the team employed throughout stages of their 2012 campaign has been re-purposed in the W04's layout. The tail or overhang has been re-orientated and raised to better utilise the effects of the Coanda system as the team struggled when they first introduced it last season. The Coke Bottle area affords good room for airflow with what looks like a scalloping of the floor leading the starter motor area making for gains in the diffuser. In the lower image also notice the curved vertical floor strake which should create an elongated vortex between the floor and tyre helping to seal the diffuser by manipulating the exhaust plumes reach. We can also see that the team have adopted a Tyre Squirt reducing slot ahead of the rear wheel to further aid in this area, however in order for this to be legal there must be a break in the floor which from the images we have of this area I can't see one yet.
From this aerial view it would appear that Mercedes like McLaren, Force India, Ferrari and Sauber have also followed Red Bull's lead in the adoption of using the Lower Wishbone to shroud the halfshafts negating the Magnus effect and how it effects the exhaust plume.
From the outset the W04 looks like a solid re-interpretation of the W03 we will just have to wait to see if Mercedes continue to assess the DRD they tested last season and as we can see from the last image they do have a centralised mounting hanger on the underside of the mainplane.
Check back throughout the day, as more images are revealed I'll undoubtedly pick up on more details