Sevenfold
Member
Publishers are pretty influential when it comes to this though. Not many would support giving away free content the way Paradox is known to.
The relationship seems to work between Paradox and their dev teams. As the artists work dries up as release approaches with all the assets well in place, the artists start making different skins (as an example) and Paradox release them as cheap DLC. It's a gamble on their part really, if the game tanks (I know) they lose out, and the (albeit often justified) DLC hate seems to overshadow the fact that people need to pay bills.