Provide assets for modders
I am building a game with mod support in mind. That will propably be achieved by using assetbundles. The Problem I'm facing is, how to provide assets for modders for creating maps, so they don't have to do everything themselves. I cannot just hand them an assetbundle with the assets I used for creating the existing maps, because I bought some of them on the asset store and can't just hand them out (they could be used anywhere) and it would propably lead to duplicate materials, textures, prefabs, etc.
So I thing I might have to build a modding tool for creating maps. How would I do this? The approach with assetbundles is just so easy, because modders would just use Unity. Now I would have to build a 3D level editor myself, or does Unity have options for that?