Yes, it makes you wonder what will happen next. I think it will take some imaginative thinking to put more passengers through the terminal and CTA. Maybe that 18 million is the theoretical limit as that figure came from somewhere and it is better to spend the money once to max out its potential rather than alter again what is going in now.
I think easyjet will move their HQ out of the CTA at some point as they are short of office space. They also now have no parking apart from a few spaces outside their HQ. The next question would be do they keep the hangar for aircraft maintenance?