I doubt it. Consider the high wing loading, high drag, and lack of certain control surfaces. Any power loss will result in a quick stall and unrecoverable spin. Most of those powered lift aircraft rely on a mix of redundant systems plus a ballistic recovery parachute for flight safety.

I guess the cutoff is if you can maintain a sink rate low enough to make a landing without killing/severely injuring passengers in an engine-out scenario.

I would expect most of these "scaled up quadcopter" companies to incorporate an emergency parachute system to handle similar to a Cirrus CAPS.