I would not just to conclusions. The temperature cockpit rules will be relaxed. According to
Bruno Farmin it might be possible to achieve them
without air conditioning system.
With the smaller engines, the extra weight of a coupe is no longer an issue. The Lola B09/80 proves that you can build a LMP2 coupe that weighs 825 kg.
According to
http://www.mulsannescorner.com/newssept09.html the better aero of a coupe is worth 5 km/h in top speed.