Santito, the extension of the runway was debated at length between the 70's and the early 90's. Of course during this time the airport was tiny compared to todays traffic and the cost and planning problems meant it wasn't considered viable. The main problem is that Feltham Common is protected common ground, i.e, anybody can graze their sheep on it, but not build a runway! Over the years various plans were forthcoming looking at a tunnel for the A38. The airport does own the ground immediately over the road. Some of the options were looked at in the expansion report. The most likely option would be a starter strip back to where the road is now thus not having to undertake a massive legal/
PR battle for the Common. Clearly the view that has been taken by the airport is that the future lies in the 787, which is a fair one. The new 747 has about 15 orders and obviously the airport will never take an A380! So the general future is the 777 and the 787/A350. They have been assured by Boeing that the 787 will operate from the current runway direct to Florida/ Middle East. So there is little point in lengthening the current strip. I presume that Emirates/other middle eastern carriers will buy the 787/350 at some point as a replacement for the 330 which may open up those routes.