Rinky,
Once all these aircraft have landed off parallel approaches what is going to happen to them ?? As I tell the aircraft when they ask me the reason for the delay at Heathrow - too many planes, not enough concrete.
As to another runway, don't the BAA own a lot of the land between the A4 & M4, and I think if you look carefully there are gaps in the A4 developments to allow taxiways from LHR to LHR North !!!!! In fact the BA complex (Ayling Island) would appear to be a ready built Terminal 6...
Wait and see...