No idea. It's almost certainly cheaper to use the existing motor (no new redesign), and the Enertia Plus is targeting a significantly cheaper price point than (say) the $11500 2012 Zero S ZF6. Which has a smaller battery, if we want to get into size-measuring contests..
I'd love to see a range contest between the E+ and the ZF6 S. S has a little less battery, but has a purportedly very efficient new motor and brake regen.
I expect to see the same motor, but I'd love to see a new motor.. or even the existing motor hot-rodded a little!