It's been discussed, but never makes the priority list
It would have to be a generic brand or something we already have licensing for (Ford, Chevy, Nissan), so it does limit our options.
So pretty much the Chevy/Ford licensing is for some reason not allowing for licensed Sonic and/or Fiesta bodies? (nevermind the Dart, I can see why you might have problems there.) That's a bummer. At the very least, how about a high performance (Read: Durability) body that can be passed off as one with some custom decals and a cool paintjob. Either way, I hope you eventually get clearance for those, They would rock!
EDIT: I would love to see you all get creative with Nissan