I'm very disappointed Valve have screwed this up; after seeing everything un-fold and reading up on it more I've definitely changed my opinion on the matter, and for the first time I actively dislike what Valve's trying here. I gave them the benefit of the doubt, but, I'm just not sold at all.
The concept is still great, allowing content creators to charge for things they work hard on. You look at all those games like Garry's Mod, Red Orchestra, Dear Esther, and Counter-Strike, full stand-alone titles we pay for that began their lives as free mods for existing games, and I think it's great people who put in such hard work get something out of it. I see no issue with that at all.
But, it's just not working in this format. It's a trainwreck. For a start I think unveiling it with an existing game was a huge mistake, it should have been some kind of experimental launch feature with Left 4 Dead 3, rather than slapping price tags onto existing free stuff. People will happily buy map packs for online games like Call of Duty, even on PC where there's free mods, so I think people would be accepting of map packs which feature high-quality maps the community made instead of just official ones. Pack a few of the best ones together, sell them as a reasonably priced downloadable map pack and give the creators the lion's share of the revenue. Could even release these packs on consoles, too. I'd be happy to see that! It'd be an easy way to continue to add lots of content into a game too, just let the community do it and see they get rewarded for it. Valve even did it with CS:GO and do it all the time with Dota 2/Team Fortress 2. And you know any content is tested and working before being added and just as high quality as you'd expect from official DLC, which you don't have the assurance of when it comes to paid mods on this Workshop.
Maybe Valve can rescue it, but, I guess we'll have to wait and see. But right now, I definitely won't be supporting it. This is them moving on their original vision of Steam becoming the community's tool, but I still don't think there'll ever be a time Valve moderation and regulation won't be necessary