The dome on the e46 M3 was for the EGR valve in between the manifold and the valve cover. It worked out well (cause it looks cool), but anyone who uses a regular e46 hood on an M3 will tell you the clearance is much closer to the valve.
That is also why a regular strut brace for a Z4 will not fit a s54 Z4 car.
I am thinking two different engines and they still cant decide which one to use. Man, talk about cutting it down to the wire. BMW still needs time to get with suppliers and budget forecasts for MY production. They should have been done with an engine decision by now....unless this is the Hydrogen powered M5....