That's right, I said it.
Lets get some skins that change the element of the heroes. The abilities function the same, but Igorok, for example, wearing a Fire skin would hit with a "Magma Thump" or something and instead of being "frozen" enemies would be "firetrapped". It wouldn't be a purely cosmetic change. a Fire igorok would be strong against Nature heros for instance.
The skins themselves can be released slowly over time and give people something to work towards acquiring.