Recently I got L4D2 for when it was free on Christmas. I really love it. It was the first time I had used the Steam workshop. It's an amazing concept. I was curious about it. I know that sometime soon (I'm hoping
that PVKII will be switching to the new version of the Source engine, which I believe would be using VPKs. There's a lot of good custom content on GAMEBANANA, but is usually found if you're specifically looking for it.
Based on how the system works with L4D2 and using VPKs, it would seem like a great content system. It may also encourage more people to do stuff and contribute. It would be easily available to people, attract some more people to the community, and I don't see any real downside to it. It doesn't seem to me like it'd be real difficult to implement, though I could be wrong. I believe I've seen some free HL2 mods that had the Steam workshop capability so I don't know if that's a problem.
Just curious is all. Seems like it would be a great place to grow the community.