Silver, if (and it's a big if) your analysis is correct, the replacement airport has to be accessible to the whole country, not stuck in the middle of nowhere.
In other words it needs to be north or west of LHR and not east.
You are forgetting that Silver Boris still needs to serve London, so it has to be close to London. The obvious position for Silver-Boris would be NW London, but that is simply no longer possible, both in terms of cost, land availability and noise disruption.
The only possibility in today's overcrowded environment is the Thames estuary. But remember, the new airport has to be well-connected, but not just to the UK but also to NW Europe. This is why the Thames location is an asset, because it can then link directly to Amsterdam, Brussels and Paris (by TGV).
Regards linking to the rest of the UK - if Cross-Rail and HS2 do not link up with the Chunnel line and also with the Silver-Boris in the Thames Estuary, then someone needs shooting.
Seriously - these are perhaps the biggest infrastructure projects of this century, that will effect the lives of the next five or more generations, and if some stupid planner get this wrong, the entire nation will suffer for centuries afterwards. These decisions are that important. We cannot have HS2 terminating 2km from the Chunnel, and the Chunnel terminating 2km from Cross-rail, and anyone planning such a national debacle need to face the full consequences of their stupidity.
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