At first, this idea seems brilliant. A simple, easy way to integrate mods into your game without having to download unofficial third-party programs, or having to scroll through the Nexus hoping you come across something that catches your eye. But then it clicked...
Bandwidth doesn't come cheap, and Valve surely aren't providing this service out of their kindness of their hearts. At what point will they do a 180 and start charging for mods when it starts to burn a hole in their pockets? It'll be "Horse Armour" all over again... but this time making money off of people who don't even work for them. Not only that, but the Nexus was pretty indiscriminate in whatever their users upload, so what's to stop Valve from saying that certain content isn't "family friendly" and therefore banned from distribution?
Really, like a lot of things concerning Skyrim at the moment, some things are better off just left alone as they are.
If X mod is deemed not to be distributed over Valve's systems / bandwidth... then who cares? It's essentially the same thing as not being able to discuss certain mods here on these forums.
I highly doubt Valve will ever charge for user-created content
without getting the modder's permission first. It would raise a whole lot of ethical and legal trouble, and it's totally antithetical to what Valve has done in the past.
Look, I don't want to go off-topic, but the hats and TF Store took the game in the wrong direction. I'll concede that yeah, the game is free now, but the last time I played it almost half the server I joined was AFK just trading and spamming the chat. And no, they aren't cosmetic, many of them affect the properties of the game. They're "free" in the same way winning a lottery is "free", you still need to pay for keys to unlock crates.
*Yawn* Play on a different server, then. There's only several thousand of them or something.
Hats don't affect anything in the game. Weapons, yes. Hats, no. They made a mistake once with hats that affected stats, but that was a year or so ago.