Depend on what you put up and in what data/file format and with what properties (like polygon count, texture size and so on). Would be the easiest if your stuff is more or less "game ready", because you make your stuff similar to how BE did the game components. But the workshop is not here now and we are not sure if it ever will be. And if so, things like skins would be much easier than new models and things that would need new animations. And even with skins, BE would still need to do some coding to implement your stuff into the game.