One of the features that we are concentrating on for Euro Truck Simulator 2 is customization of trucks. Here is an example:
Euro Truck Simulator 2 vehicle customization
We are trying to design the system to be very flexible. In addition to the tuning parts that the game will come with and that will be available "out of the box," it should be possible to cleanly add more parts via mods, without making a mess of it. The game should recognize additional parts and offer them for purchase in addition to the original ones.