I saw some artist's renderings of a big, grand security checkpoint planned for the new terminal -- but I don't think it would be practical to funnel all airport traffic through there. For one thing they'd have to reroute the North and South Satellite trains so they pulled up adjacent to the central checkpoint. And anyway this was before 9/11. Security takes more time now.

It looks to me as if the new arrangement for the D and N gates is here to stay -- they're refurbishing the train "station" down there, directly below the current security checkpoint. The new landside terminal currently being built could accommodate a similarly big checkpoint for the A and S gates, but the B and C concourses are still well separate. I don't know how you'd consolidate security for B and C short of "sterilizing" all space behind the main terminal ticket counters, which would leave no space (or food, or shopping) for meeters and greeters. Meet-and-greeter clogging is already a serious issue in the terminal since 9/11.

So on balance I can't see how they'd go to less than four checkpoints.

As for the train, there are definitely plans for a pure airside shuttle train among the terminals. There's a new platform for one under the D gates, opposite the departure point for the North Satellite train.

The current trains used to run in three-stop loops: Main Terminal -- North Satellite -- C Concourse and Main Terminal -- South Satellite -- B Concourse. That helped with codeshare transfers, etc. But after 9/11 they cut out the C and B Concourse stops, I guess because they only want you to go to the pier or satellite used by your airline.