The issues with electric planes have been beat to death here
Where? Slashdot? I can't recall ever reading about electric flight beyond drones, though I'm sure there has to have been some in the past.
The main problems are batteries, not electric propulsion itself. That batteries are far heavier that fuel on a lbs/kw basis, plus you don't get the bonus of the plane getting lighter the longer it flies. And high bypass turbines on planes aren't as inefficient in use as the ICE in cars (and planes are much more weight sensitive than cars) so you can't trade weight and drivetrain efficiency for useful range like you can in electric cars.
Also, for commercial planes they spend very little time on the ground between flights; so you don't have time to recharge batteries. So you're looking at a battery swap technology as well to keep the turnaround time comparable to refueling.
That said, if the distributed electric propulsion is as efficient as NASA thinks it might still be a net win even if you have to pair up the electric motor and prop placement of this X-57 with an onboard electric generator. In which case all the downsides of batteries are irrelevant. (Then you could look into whether a hybrid design with a some batteries and a smaller generator made sense)