Source code that Valve put out looks to be somewhat sanitized compared to the sdk2013 code leak. I did a quick comparison of the "shared" tf folder between both. There's still some stuff in the Valve release. I spotted a weapon script for a boomerang that I also saw in the leak. But I don't see the "staging" blocks in Valve's tf_shareddefs.cpp that are present in the leaks copy of the same file.
Them allowing tf mods onto the steam store is not what I was expecting to happen, so that caught me by surprise. Would have been infinitely funnier had they cease & desisted the mods, but I digress. The blog post mentions stuff about player inventories so I think Valve is trying to suggest that someone could make a new custom client that can interface with your actual tf2 inventory.
It's a good thing they specifically noted that using workshop cosmetic/weapon models in a mod, and trying to earn money with said mod, or profit off those assets, is not allowed. To clarify, you can use those workshop assets as long as your mod is 100% free.
Well folks, it's official. Valve doesn't give a shit about TF2.
E: also, there's now a big opportunity to make a custom client pre-packed with all sorts of model/texture fixes from the community along with other interface fixes and such.