I don't know why they're adding this before item trading.
I wouldn't count on trading ever comming out tbh. Valve have griefed enough about idlers, the instant something's introduced that has the potential to trade hats for real cash they'll drop a toaster in their bath.
And I don't think they mean re-designing key features of weapons, think they're merely talking about changing the skins - which is awesome imo

Technical Info
* Keep the polycount similar to what's already in the game. Keeping hats under 800 polygons, and weapons under 8,000.
* Texture sizes should not be larger than 512x512. For hats, 256x256 is usually large enough.
Hats made everyone unique, then everyone got them - now v.rare personalised weapons? Sounds pro :>
EDIT: Just seen this, maybe they do mean whole new weapons :S
Use the definition indices for item types, attribute types, and quality levels in the JSON feed to index into the items_game.txt dictionary, and you're good to go. Note that it will respect the privacy settings on steam profiles, so it won't report the inventories of players who've marked the profile as private.