I don't think that having an airside connection between A and G is itself what's driving the redesign plan. They want to consolidate security and increase revenue of the restaurant/retail space that is currently landside. Maybe there were mistakes in the original design, but security requirements and procedures have gotten much more complicated since then. And that has made passengers less willing to linger in landside areas before their flights. Get through security and then maybe shop/dine/eat.

When it finally happens, there probably won't be that many passengers who go directly between A and G gate areas. Connecting domestic-international passengers will mostly be going from T3 to G, and from T1 to A. If your connection is international-international or international-domestic you don't have the option of staying airside.