The idea has merit. Many other games employ a similar method of content creation, allowing players to make stuff and then highly rated items get checked over by devs and potentially added to the game.

The issues to work out include:

1) Finding the time and resources to have someone continually checking submissions. (Not to mention, that it would still take some time to then add things to the game)

2) Compensating players for their work (Since, technically, it's their stuff. There's legal action possible if SE are profiting of their work. Many other games get around this by adding them to cash shops and giving the creator a portion of the sales... But how would that work in XIV? Would people want all the fan-made stuff to end up on the mogstation?)

3) Setting up an adequate place for people to show off their creations and for players to approve/disapprove of things to find the highly rated stuff to check using actual dev time (As well as filtering out all the poor creations such as tasteless 18+ content, copyrighted content or things that are just not a good fit for the theme of Eorzea (More so than what already makes it into the game >.>))

4) SE is a business. How much profit will this get them?

I mean, personally, I think it could be a cool idea. If players are capable of making high quality content using the same tools that the devs use and are willing to put in the time to do so, then it would be neat if they could work on additional content while the devs continue to do their own work.