MAN777,
For the time being at least, LHR is still Europe's busiest airport. London's airports combined still keep the world aviation capital title (by pax numbers).
capacity can be maintained by use of A380s
Not feasible for shorter routes, where frequency is needed, and load times would prevent fast turnaround. But in principle I agree - larger aircraft means more pax from same runway, but still creates issues with wake, and land still needs to be found for the terminals. I think switching 737-500s to 800s, sacrificing some shorthaul frequencies for larger a/c on long haul more likely change.
never ending desire to have point to point from London to every point on the world
This is a natural desire anywhere, and remember that whether ptp or connecting, a seat is still occupied - and the hop to AMS or CDG for conx uses MORE runway space than direct in a 777 going direct as the hop uses a smaller aicraft.
Yet, despite rising fuel costs, despite UK APD being a notch higher than everywhere else, people still want to come and go from London. LGW is seeing a big uptake in Asian routes, and it has room to expand in a way which is far more cost effective and politically do-able than either a new airport-on-sea or at LHR.
Don't forget that UK regional airports have done very well out of the growth in locost carriers - I remember EDI's route map in my days as a student there until '98, very few European cities served directly, now look at it, not to mention EWR too.