We've already got an enormous amount of Art we can use for skins.

Splinterlands Art contest winners. Get the permission of the artist, or make it a condition of entry that winning entries will be licensed by Splinterlands and receive an x% royalty on skin sales.

The mechanics might be a difficult thing to implement (as the devs are busy working on other things) - but the pay off for the community and the artists involved is ongoing, instead of a once upon a time prize.