None of what is being mentioned here (apart from cards) can be added straight away just because we want that.
Workshop needs proper integration so that there was a possibility to upload stuff to Steam servers using the game client. The only thing that's worth being uploaded to the Workshop are 3d item objects, so some tool will have to be added (in case it's decided to add anything).
Market is even more complicated as it will basically make TC worthless as everyone will be just trading items for cents via Steam. And, once again, the coding part.