I know LHR has some of the longest runways at about 4km, but as there is waste ground on the end of 27R, why not extend by an additional 1km each end?
With a 6km+ long runway you could have simultaneous arrivals and departures, if the departures line-up from the mid point.
Oh is that the waste ground that includes multiple staff car parks (PEX) as well as passenger car parks and further to the east from them is Hounslow and residential housing. Rather dismissive to call it waste ground, bit of fact checking and respect in order here I think.
