The Elgin-O'Hare is already under construction to the West Terminal site.
It would be a waste to build a whole new set of infrastructure for a new terminal on the east side.
The only concern I have about the West Terminal is inter-terminal transfers, but I've always thought the problem could be solved inexpensively if you planned the airfield around a surface busway. The busway would be secureside with enclosed heated shelters like the one at Heathrow, so travelers could go through security on whichever side of the airport was most convenient, then take the bus over to each terminal on the west side.
Threaded Mode