My wife has been watching me happily smashing up cars and suggested how much more physics based hilarity and mayhem could be enjoyed if there was an option for cars to pull trailers/caravans etc. And I thought that was a great idea! Imagine a nice flimsy caravan (similar to the box van) wobbling around behind your vehicle as you bounce around the maps. Imagine the carnage! Alternatively if you're more into the driving simulation, imagine the challenge of successfully towing a trailer around say Dry Rock Island....
I knew trucks were planned, but I haven't heard anything about buses. I guarantee that someone in the community will make one, but did the devs say anything about making an official one?
By official do you mean Gabester made? But really anything with wheels that doesn't float or fly at the moment is possible.