On a Venn diagram, the modding and trucking communities are pretty much one circle. What Truck Simulator player doesn't want to customise their rig or convoy with thousands of other drivers online? Yes, modding is alive and well in SCS' sims, but the devs are set on making things easier still by implementing Steam Workshop support.
The update will come as part of patch 1.23 for Euro Truck Simulator 2 and patch 1.2 for American Truck Simulator—they haven't been dated beyond "a couple of weeks" away yet, and they'll go through public beta tests before going live for good.
To foster the creative spirit, SCS is also putting together a Wiki full of guides and info to get your started in the modding business. That's in addition to a specialised SCS Workshop Uploader tool that'll help you get them online for the world to see.