When Valve began integrating paid mods into the Steam Workshop with The Elder Scrolls V: Skyrim, the gaming community replied with anger, some went as far as sending death threats to Gabe Newell. The general concensus was paid mods on Steam were a bad idea.

The intentions behind the paid mod program was to give money to the individuals that spent so much time creating mods for games and making them available to everyone.

Both Valve and Bethesda quickly decided to scrape the idea after implementing it, saying that they shouldn't have attempted to integrate the paid modding program into such an established community such as Skyrim. Note that they didn't say it was a bad idea in general, just that they shouldn't have started with Skyrim.

It is being reported that terminology in the Steam Workshop has changed, suggesting that paid mods are making a comeback. According to Game Debate, any creator that heads into their Steam Workshop and check out an item will be met with a message that says:

“You can subscribe to this item for free because you are the creator or listed as a contributor.”

While it is a subtle change, suggesting that you can subscribe to an item for free implies that other items will not be free. No official word has released on the subject, but it was questioned if the paid mod program on Steam was why the Fallout 4 Creation Kit was taking so long.

Bethesda and Valve did originally agree to attempt the program last year, with Fallout 4's community not as established as the Skyrim community… It could be the next community to have the paid mod program attempted on it.

This has not been verified by Valve or Bethesda, we have reached out to both for a response.