Originally Posted by
exerda
IIRC they had pie-in-the-sky plans to add multiple new midfield concourses

They still do! If I had to guess I would say completion would be complete in 2150 or so. Unsure what traffic forecasting model they are using that shows future traffic would require the construction of two additional piers.
The gray line in the middle is the sterile APM line directly connecting local traffic to the IAB. I believe they may have done preliminary tunneling on that project when the Aerotrain was first constructed.