I'm not convinced that this is an Esprit mule. It simply makes no sense for Lotus to use the short wheelbase Exige as a test mule for a much larger car when they have a much better option available - The Evora. The Evora is almost exactly the right size - the rear passenger area providing space for the V8 Esprit engine.
This car is more likely to be a project for another manufacturer (Lotus are always keen to sell to other manufacturers e.g. VX220) or a racing version of the Exige, or even the next generation Elise!
BTW the source of the 275 - 325bhp per tonne Esprit power to weight figure is here (in a graph in the presentation slides)
http://www.scribd.com/doc/21734205/Evora-Vva