I'd imagine that Sarfend would die a death as would most of the nearby airports once the super airport was up and running, especially if fast transport links were included to and from civilisation. The air traffic around London would sure change, make a LOT of blighted residents happier and (no doubt) cause a whole set of others to curse the new airport.
I do wonder though, how will they negociate with millions of migrating birds that use the Thames Estuary as a resting/feeding ground, especially as they've been doing this for perhaps thousands of years and might not understand the implication of FOD and aircraft powerplants
The proposed airport makes sense, especially on an architects drawing board and a politicians manifest, but in reality.....well, just look at all the large building projects started by the UK for an indication.
SHJ