As I said, governments of both persuasions, have never allowed forward planning. They did not allow the site to be expanded and they did not allow a brand new site - other than proposing them in silly places like mud flats and far out to the East or even far South East. A new site that was further along the M4 could be have been set up 25 years ago but it wasn't and now the cost would be horrible.
The airport is trapped and I am doubtful that the Northern expansion through Sipson will actually go ahead. If it does, I suggest that the operation of the place will remain as chaotic as it is now.