Can quadrotors be used for commercial passenger flights?
The three most important factors in passenger air travel are safety, safety &amp; safety. So that is where most of the questions will focus on, and where most of the engineering effort will be put into. Couple of questions:


Artificial stability: what happens if the stability circuit breaks down?
What happens if one of the motors fails, for instance one of the big aft ones? Can the craft still stay upright or does it topple over? If it stays upright, can the remaining motors still provide enough lift to keep the craft flying?
What happens if the battery runs down or fails during flight?


These are redundancy problems that need to be solved. Any system that causes an unsafe situation when it fails must have a redundant layout. So at least a penticopter instead of a quadcopter: upon engine failure, 4 props can safely land the craft.

The redeeming feature for quadcopter is ease of manoeuvring with variable rotational speed per propeller, instead of having to make a swash plate arrangement. But light single rotor helicopters have been around for a long time and the technology is mature - I don't see what particular problem the quadcopter can solve that for instance an R44 might have. 

On your questions:


Q1 Noise: yes electric motors are nice and quiet, and the shrouds shield noisy tips in most directions.
Q2 Regenerate energy: it can only do that during authoritative descent, which would be frighteningly fast due to the relatively small total rotor disk area.
Q3 Not a UAV: sure, tilt rotors exist already






Edit: the propulsion system you draw is not so revolutionary. If you travel to Niagara Aerospace Museum, you can see the X-22, built in 1967.



From a comment:


  •I have had one rotor fail (larger) and be able to land the aircraft safely, even maintain a hover but not climb. Aircraft does not topple in simulations, software used Xplane 10 and 11 ultra releastic. – Robert Gomez


That is a claim that sounds hollow. It depends on the location of the centre of gravity: if it is within the triangle formed by the remaining three rotors, it will stay upright. Picture an X cross connecting fwd left - right aft, fwd right - left aft. 


If CoG is behind the middle point of the cross, either one of the front rotors can fail and the craft will fly stable on the remaining rotors, because CoG is within the triangle formed by the operational rotors. But not when one of the aft rotors fail.
If CoG is forward of cross centre, either one of the aft rotors can fail. But not a front rotor.
If CoG is exactly at cross centre, the rotor diagonally opposite the failed rotor cannot exert thrust otherwise the craft will roll. So one rotor fails means only two can be operational.