Skins Based on non-Riot owned IP.

Has Riot ever considered making "sponsored" or legally recognized skins based on other fictional works? Something along the lines of Grungy Nunu but created with the original content's creator's permission, like an actual collaboration between Riot and another company. References are cute, but they appear very little in League (references to non-LoL related content, that is). How hard would it be to make something like that, both in design and in getting the "ok" from another company? Has it ever been considered?