So, lets say that I want to make a skin. If it meets your quality standards and fits with League, would you be willing to put a skin on the store for everyone to buy and see? I mean, custom skins are great and all, but it's not like anyone can admire some of the actually good ones. Anyway, if this is possible, I, as well as many others, I'm sure, would be willing to make a skin for a champion I very much enjoy.
Headhunter Caitlyn is from a player design
No. Understand that Riot make a huge chunk of their profits off the sale of skins. By using user made skins, they would have to give a percentage of their profits to the original creator, and why do that when they could just release the skin themselves and keep all the profit? This isn't a faceless corporation thing, this is just a basic business practice.
The reason why Valve are able to do something like what you're asking for with DotA is because it friggen Valve. They have more money than Riot could ever hope for. The money they don't make on their skins costs them nothing in the grand scheme.
