>>There are already people doing this sort of commute but typically they are higher end executives or self employed who can dictate their own timetables. So I could but its not doable for the bulk of the population.

Yes, but things change. Mobile telephony was unavailable to the bulk of the population until the mid 1990s. Within a decade, most adults in the first world had access to mobile telephony. The state of play in 1992 did not predict events in 2002.

>>300m is vertical separation . I'd be very scared if jets flying over my house where 300m apart laterally. I think lateral when approaching to land the minimum is about 3 miles.

Even focusing on fixed wing aircraft: many here will have landed at a busy airport and seen other aircraft flying much closer than 3 miles away. The point is that thinking in 3D, fixed wing aircraft can safely fly with only 300m separation or theoretically less if there's special airport control radar or automation. Also consider those military midair refueling exercises with almost no separation. Of course drones are not fixed wing and a better comparison would be helicopters and more maneuverable flying machines that can land on a dime. I nominated a generous 5m separation for drones with split second reactions and 3 dimensions in which to avert collision, yielding 40,000 simultaneous drone movements in each square km slice of space. That's a lot of Amazon deliveries. ;-)