Monetizing game modding?! Nooo
That's what Roblox is basically already doing. Except it's more like "create your own game from these blocks" kind of thing, the content there seems to be of remixing lot of existing ideas and concepts. The monetization apparently works there: https://venturebeat.com/2017/07/21/the-deanbeat-robloxs-kid-...
First thing I thought of was Skyrim modding, modding through steam workshops(e.g. rocket league), and garrys mod