Modding have always been a big part of gaming world as we know it. Many of the full-fledged games started as mods of some popular game. After which then got identity on their own and were made a standalone games. Team Fortress 2, DOTA 2, Portal, Counter Strike etc. are some of the prime example of the games made from some mod previously developed. Recently several months ago Valve stirred some water by implementing paid modding in game Skyrim. Obviously backlash was huge so they had to take the decision back in several weeks but it did made some talks in gaming community if it can happen I future or not.