The motivation is to be "pure Lotus," and that requires building not just the chassis, but the engine, according to the new mandate--though fans of the Toyota-powered Elise and Exige models might disagree with that somewhat.
Whichever side of the Lotus fence you're on, you have to admit, the promise of the new Esprit is tantalizing. A return to the Lotus supercars of old, through a modern lens of design, performance, and (hopefully) reliability would be a welcome challenge to the current Italian, German, and occasionally American or Japanese status quo.