There are specific dimension guidelines which must be adhered to for the LMP1s. Nissan cannot turn up with a GT-R retrofit with it's new hybrid drivetrain and take part in the class.
Performance is the priority and ultimate performance cannot be achieved without bespoke purpose-built bodywork to reduce drag while affording a balance of downforce.
Yes, the Nissan will be the least attractive 2015 LMP but I am delighted to see something different. The WEC is my favourite series so perhaps I'm biased but seeing top-tier motorsport allowing significant creative freedom, with great balance of performance management, is refreshing nowadays.
I only see the WEC getting stronger in the coming years and if the latest rumours of a Maserati programme, as opposed to Ferrari, bare fruit us fans could find ourselves in another golden age of sports-car racing.