In the wake of the whole debacle with Valve and Bethesda's plan on charging people for mods for The Elder Scrolls V: Skyrim, John Romero has revealed that Id Software (Doom, Quake, Rage) had similar plans some 20 years ago, although there were a few important differences.
In an interview with Games Industry, he says: "I've always believed that mod makers should be able to make money from their creations."
Instead of people actually paying for the mods, Id Software had a different idea to pay modders who did popular additions:
"In 1995, while we were making Quake, we had the idea to start a company called Id Net. This company would be the portal that players would connect to and play other mod maker's creations. It was to be a curated site, levels and mods chosen by us at Id, and if we put your content on our network we would pay you an amount equal to the traffic that your content drove to the site. The idea was that players would log in and be in a big level that felt like a castle with lots of doorway portals and signage that explained where you were going and what was there."
Quite how the future of paid mods will pan out is difficult to say. There's obviously some kind of monetisation coming, but exactly how this will work is still very much unknown. Perhaps a solution similar to the one consider by Id would work?