I think the third runway and T6 would help, if the government restricts capacity. If LHR had spare capacity and additional resources then it would not be the total nightmare it is the moment something goes wrong. Most of the rolling small delays that plague all flights are down to one small thing that happened earlier in the day. There is no spare capacity to pull it back and so the delay stays. Even worse during fog etc the whole place totally falls apart and when the weather does start to improve it takes LHR longer to recover because it was so overly busy to begin with. Hopefully the BAA and the government will put in spare capacity that will enable LHR to operate as a busy, but stable international hub.