The basic concept behind this idea would involve a step-by-step process to avoid any form of copyright infringement.
Step 1: 4J Studios could introduce a website or perhaps just an added section here, where users could design their own versions of block textures and mob/player skins. In order to make a full texture or skin pack would require the user to provide new texture and skins for each block and mob while skin packs would require a minimum of 25 skin designs.
Step 2: Limitations to protect copyright work while maintaining the usefulness of current and future texture and skin packs available through 4J Studios. This limitation would prevent any form of image insertion or download. The creator must create a unique set in order to submit a pack. This does not limit the user from just copying any given art form which is where the next step comes in.
Step 3:4J Studios art team review of submitted packs. This wouldn't require anything more than the art team to review and approve or deny. The decision would be solely on the art team. Any copyright or inappropriate work could be caught rather easily.
Step 4: Users must electronically verify consent to 4J Studios that their creation may be used, modified or removed at the discretion of 4J Studios. Also recognition that the user will in no way receive any form of financial gain or royalties regarding their creation. Once submitted, the content becomes property of 4J Studios and Microsoft.
Step 5: To prevent overflow, a vote would be held every 3 months on any number of texture or skin packs that 4J Studios felt were deserving. The amount of content to be voted on and the amount that passes a vote would also be 4J Studios sole discretion with the ability to add, modify or remove any content even after a pass in votes. Votes could be held on social media and any other platform 4J Studios deems fit.
Step 6: Upon approval and pass, content shall be initiated into the update file where it will undergo the regular required testing and then denied or approved on Microsoft's end.
Step 7: Download and enjoy. User created content can be sold at standard pricing or any amount deemed fair.