well apart from Hong Kong, doing this would not close LHR. It would just open up a new airport.
Not blue sky thinking at all. Just keeping his name in the papers and getting the dicsussion ready for when the Planning comes for the next runway at LHR and he gets to sign it saying yes. Always good to have the evidence of why it can't go elsewhere at your fingertips courtesy of some good old fashioned PR.
Alternatively, if the governments white paper on aviation for the next 30years, seems to run out of cpacity before it should, then they will pay for something like this, which has already been proposed in that very same document, and Boris will be seen as a visionary.
No real downside here is there?
And seeing as LGW is up for sale, and BAA need a new runway at LHR, guess whats around the corner as far as planning applications is concerned? The 3rd runway was always going to happen here as T5 was built to help LHR handle 90m pax a year, and yet the runways are at about 98% capacity. So why have extra passenger capacity?
Its just another part of the jigsaw coming together.
(What would they use to build this new island? not wanting to expose the only real problem it faces!)