The third and/or fourth runway for LHR is all very well to cope with increased air traffic but significant expenditure is required on the infrastructure surrounding LHR and beyond.
The route in to London would need at least an 8 lane or 10 lane motorway, further lane expansion for the M25, M4 from the west and M3 from the south west. That will mean a lot of houses will required to be knocked down to make way for all this development.
I think the east London Hub Airport proposal would not give the substantial benefits to the economy that an expanded LHR would.