When Bethesda and Valve announced paid mods for The Elder Scrolls V: Skyrim, the reaction was negative, and it was quickly retracted. Some have suspected the idea would come back with Fallout 4, but as of right now that doesn't appear to be the case.
German publication Spiegel Online, the digital version of Der Spiegel, asked game director Todd Howard about paid mods towards the end of their interview.
The version I'm pasting below comes through a Google translation, so excuse the awkward phrasing, but I had a German speaker look at the text. It checked out.
SPIEGEL ONLINE: In the Microsoft press conference was announced that created by PC Fan extensions to run on the Xbox One. If you have to pay for some mods? In "Skyrim" Bethesda has experimented with a Mod-payment option , which was withdrawn after fan protests.
Howard: How long was the online payment system? 24 Hours? I can only speak for the present time, but currently there are no plans for a payment system.
Could it happen in the future? Sure. Right now, though, it seems they're playing it safe.