My idea is to have a marketplace like Unreal Tournament 2014 where people can sell their mods.Team Fotress has something similar.All mods code must be under an open source license and the most restrictive license allowed for mods and the mods assests is CC-BY-NC-SA 4.0 Free means freedom aka libre not free beer aka gratis. Cg cookie has something like this http://blendermarket.com/blender