I live in what could be called an 'outer affected area near Camberley. There was a minor protest when HAL/NATS did some trial departure routings without telling any one-apparently they only contact contiguous borough which is to put it bluntly ridiculously naive .
However the idea of aircraft closely following the exactly the same tracks on the SIDs will cause public nuisance complaints. The method used for years of aircraft for whatever reason following slightly different paths was perfectly accesptable and there were no good reasons given as to why the new method was required . One has to bear in mind that in my area there are current and retired pilots and ATCOs and numerous airline Ops staff so not only is it generally airport friendly it is also very knowledgeable. So planning the tracks for a third runway will need consultation but as Gonzo hints the way things go in the UK any current flying and ATCO staff of any seniority will be retired by the time R3 is built