Golf-Sierra, interesting questions. An aircraft like ECR-20 could provide a capacity boost from airports like London City. It won't be more quiet then a e.g. 737 currently is, but would offer better takeoff performance / steeper approaches (DLC) and airport operations would be different. An automated engine shutdown procedure would start as soon as the aircraft leaves the runways after landing.
The aircraft would arrive at the gate/parking place with the engines out. At departure there would be no pushback required and starting of the engines would be done during taxiing to the runway. It could become quiet around the gates. It seems Airbus will (finally..) do live tests next month.
http://www.dlr.de/en/desktopdefault....y-1/51_read-3/
For quick (de)boarding the ECR-20 concept has twin aisles, a mid cabin crossover and wide doors front and aft and integrated airstairs that can be deployed as soon as the aircraft halts. The aircraft taxis away as soon as the doors are closed, no more push back and engine starting procedures, saving manpower, fuel, noise and minutes.