[belorn]

The idea to sell unofficial third-party add-ons for third-party products sound generally a dangerous concept, and doing so without any quality control or responsibility sound to me as inviting destruction. If you pay for a product, and it randomly breaks at a later date because of a patch, someone is going to have to take responsibility. If its not the game developer (they didn't get paid), and its not the mod developer (its not their fault that the game got patched), its likely going to be the store who pocked 75% of the money. Add to this the infinite ways mods can interact with each other, or mods that depend on other mods, and the legal requirement to sell mods created by private people seems impossible in the best of lights.

Donations, Kickstarter, and Patreon on other hand is currently already working to provide compensation to passionate content providers. Valve could have gone this way and made it easier to donate and support modders.