I have struggled to discover what is the enabler of this concept, and why it is suddenly valid.
The only thing I can come up with is that electric motor power of multiple fixed pitch rotors has been enabled by much better gps, accelerometer, gyro, and control technology, and this in turn creates a cheaper machine with less failure modes, more opportunity for redundancy, and more opportunity for autonomous control.
Unfortunately, as evolution (and the B52) prove, we're not going to come up with a better way of accelerating air. It needs a crapload of hp. Mr Bernoulli and his friend Mr Einstien are not to be denied. Batteries are not good for a crapload of hp.
So the enabler of the air taxi is electric power. But without a battery (or other e power source) breakthrough the air taxi is stillborn. Even with a power breakthrough, its still a long long long way off due to all the other boring, (but very valid) reasons quoted in other posts. When a Tesla can go 1000 miles on a charge and be recharged in five minutes, we should start fearfully looking to the skies for some air taxis. And until then all these guys spending a ton of money proving you can scale up a quadcopter control system to people sized are wasting their time.