I think that is the current fuel farm
I can't expand the picture enough to read the terminal plan but I would say that the fuel farm is south of this presently so maybe it is a new passenger facility - crazy though that it's covered by the other insert!
The only other thing I can think of it being is the new drop off zone?
As for a new terminal, how would a dedicated domestic terminal sound? Its already by the remote stands Flybe use and would relieve some pressure off the main terminal.