I think I will go for a Steampunk Era/Civil War theme. I have a few ideas, one regarding a dishonored Confederate soldier who lost his legs in the war. He is out for blood. He's harnessed the power of steam and integrated Civil War weaponry into his vehicle. EX: Musket Volley device that unleashes dozens of bullets and shrapnel with the push of a button.
I will probably start blocking out some ideas shortly.