The Eastern Gateway is a project that has been slated for Disneyland Resort for a long time, it goes back a decade (or more) at this point.
There is a thread about it -
This can be the new spot to discuss a resurrected Eastern Gateway that should be coming this year.
forums.wdwmagic.com
Basically both Disney and Anaheim want to get all the Resort transportation and pedestrian traffic off of Harbor streets. The idea is that the Pumbaa surface lot will become a new multi-story parking structure. It will have a new transportation hub that takes traffic off of Harbor and puts it on Manchester. A new pedestrian bridge will be constructed over Harbor that leads directly into the Resort. This will remove the cross walk on Harbor, something that Anaheim has wanted to do for a very long time.
Because of Disney/Anaheim issue in the past, its now included as part of DisneylandForward.
So this is all to say that Disney is planning on using the old transportation hub for DCA expansion.