The trouble is, this won't be possible for the same reasons they've already stated in the past why they can't allow player-created FC Logos and player created images for portrait furnishings in houses, and that is the necessity that SE would have to screen every example of artwork that a player wants to use.

Because despite their best intentions, human nature being what it is, you know there would be at least one individual who would think it funny to upload something pornographic/derogatory/downright offensive, thus requiring SE to police the whole system. And because that would chew up a lot of development/community team resources that are needed elsewhere, sadly this just won't be happening.

Having said that, SE are running 'create your own armour' competitions where the winning entry has their item actually added into the game, so that is close. But sadly a full 'player-generated content' system just is not possible I'm afraid.