Valve has announced that they will be allowing content creators to charge for workshop mods:
The Steam Workshop has always been a great place for sharing mods, maps, and all kinds of items that you’ve created. Now it's also a great place for selling those creations. With a new, streamlined process for listing and selling your creations, the Steam Workshop now supports buying mods directly from the Workshop, to be immediately usable in game. Discover the best new mods for your game and enable the creators to continue making new items and experiences.
While this seems a great way to incentivize the creation of more and better mods, of course not all gamers are happy about it. [venturebeat.com - Warning: lots of javascript]
(Score: 2) by vux984 on Saturday April 25 2015, @12:25AM
Yeah, this should have pretty much been put through their whole green-light system or something; so if a dev wants to make his mod paid, he submits it as a new game title ("fan made DLC") and its goes through review and approval for publishing (for some threshold of quality, functionality, and lack of copyright infringement or outright plagiarism or piracy of a free mod); and the steamworkshop community modding is a separate and free thing. Otherwise the whole thing is just going to be flooded with shit and shovelware, and rip-offs.
The idea of paid "fan DLC" itself isn't necessarily a bad idea, total-conversions of games etc are pretty cool, and some mods are a lot of work, but most are just some little tweak or model or level adjustment etc... co-mixxing paid mods with the free community is taking a big dump in the pool.