I have a couple ideas
Allow a unit to respond farther than 400KM. Say I want to respond from New Jersey to Florida, Texas or even California. Despite the lengthy travel time it would add a sense of realism for National Emergencies.
And a new Unit Type: Aircraft Unit Transport. When transferring units via ground across states perhaps having aircraft trabsporting these units. It doesn't seem real but on a game standpoint may not be a bad idea. So that units transferred won't take as long.