Open world movement
Okay, nobody seems enthusiastic about my thoughts on expanding content to include image comics characters....
So ... how about vehicles? The maps of Metropolis and Gotham are bigger than the old GTA 3 map... so how about hideouts including garages, hangers, boat launches. New races, feats, a whole new level of individualized gear and collecting classic vehicles. Imagine cruising around in the batmobile, flying the blue beetles bug, cutting waves on an Atlantean speed boat.
Of course if your character wants a retro futuristic partially Brainiac assimilated rocket plane... you can design one.
This could be a huge draw to the game.
There is already the device that can make you a small batwing... but I was thinking a more ambitious scale.