TL;DR
Resource library to make modding bit more friendly.What ?
Do u can add some resource library?like images, sounds, simple mod presets to learn api fast(probably not so important), free to use and modify 3d models for mechanisms(like cars, 44 or more images for any rotateble object? rly? )
Why ?
Many of peoples who can code the mods, cant make animation and pictures for their stuff.(and keeping style of game view)if modders will have library with images and sounds, we will see alot of interesting mods with new mechanics.
images like metal debri, space trash, forgotn/broken cars, unused in game machines etc...
will be much easier to make something, if you will give to modders more resources to start, and after mod will be loved by players - make their own images and animations