Crains has a few more details today about the expansion project.
http://www.chicagobusiness.com/artic...whats-in-store
The satellite concourses will be connected by underground tunnel (likely with moving walkways) and this will include a space for two future train tracks. The tunnel will not extend to the west side of the airport, nor will the city even contemplate purchasing a train system for the tunnels until passenger numbers top 100 million for 3 consecutive years.
The article also made no mention of other landside improvements to ease the tremendous congestion on I-190 and the arrival/departure roadways. In fact this expansion will only further concentrate traffic on the T2 section of the ring. The only good news for landside is the soon-to-open CONRAC, which will at least remove most rental shuttles from the arrivals level (the lost opportunity to connect to Metra at the CONRAC is insane to me also)