I am sure someone at the airport is looking beyond 18 million passengers as that figure could be with us from around 5 or 6 years.
The terminal can still be tweaked as the infill behind check-in desks 201 to 210, which sits at a right angle to the main check-in area has been cancelled. If it did take place the space in front of those desks where the passengers queue would have been the same size as the other check-in desks making them more usable but it was no simple task to build as the infill would have to go all the way down to the basement.
It is a shame that the new pier isn't going to the south stands as holding lounges could have been built to relieve pressure on the departure lounge but I can't really see what more can be done inside the CTA.