Should the airport look to build a T4 due to the capacity restraints building on the existing footprint? Although where the new footprint would be is up for a debate. (I think the western maintenence area even though I know it would be costly moving the fuel farm.)
this would be VERY long term. It's taken them long enough to get the development on T2 going. Also with T1 scheduled for demolition, there's a large development they could put in its place.
Once both of these are done, It's either T3 expansion, or a new T4. As you've pointed out, the location would be up for discussion.
There's some argument for moving the fuel farm/ hangar areas in favour of a new terminal, but as to where these could move to remains to be seen.
An alternative would be to completely remove the Runway Visitor park and put the new terminal there, then move the Runway park to the other side of the airfield (around the Airport inn and South side viewing area
despite this, this would be 2050'esque' levels of 'long term'. and will not happen anytime soon