Silly idea.
Unacceptable noise increase. Still hopeless for rail connections. Still too compact and crowded, in airspace, taxiways and stands. Still a nightmare to get between so many different terminals, in time to catch your next flight. Still dangerous to have so many approaches over the center of a capital city.
And I a not convinced that this extra runway will generate enough domestic European flights, to enable LHR to become a proper international interlining airport. LHR will never be able to compete with AMS, unless it gives cheap enough landing and handling fees and convenience to attract the likes of Easyjet. While I am not a fan of LoCos, they do attract a lot of interlining pax going international. Unless LHR does something drastic in their economic structures, I reckon I shall be interlining through AMS for a long time yet.
In short, the UK needs a new four-runway Thames airport, or London and the UK will lose its prieminent role in international trade, aviation, politics and banking.
Silver