I know there's been some discussion on this already, but I wanted to put out some examples of how this is being done in other games.
Fight The Dragon (a game on Steam) has an Adventure Creation Kit (ACK) that is very user friendly but also allows for some very detailed complex level creations. I'd like to see something like that implemented in SK. They have systems in place to prevent farming and make sure there's an appropriate amount of monsters to treasure to health/potions ratio. Anyone else here played Fight The Dragon and used the ACK? Man, that tool on this game would be awesome!
Also, Star Trek Online is a great example IMO of both regularly released official content plus user created content via their Foundry. Their Foundry isn't nearly as user friendly as the above mentioned ACK, but I think STO has a great system in place for allowing user created content to coexist with official developer created content.
Thoughts?
Super Mario Maker is another proof of what you're saying. Only concern with user created content is levels designed to profit players handsomely, there would need to be some sort of control around that.