I've always wanted this and so have many others (that often annoy the most of us with their obsessed whining over a new TF2 pack), but ever since they made Hitman's Heatmaker for BL with its ammo system, I've wanted an edited / new TF2 weapon pack using this ammo system.
Now, we can be reasonable about this when I say, why make all of the TF2 weapons? That would take a while. Why not, if I may, make what is popular among all TF2 players? For example, the Rainblower (Something I actually found in TF2 today and killed an unaware sniper with its taunt) could be made...minus the Pyroland feature. Another thing that could be made is Pretty Boy's Pocket Pistol. But I'm not going to stand here and list them to you. I'll let you decide.
...But it would be pretty awesome if a crafting system could be made with only some simple objects such as making scrap, reclaimed, and refined metal to make other simple weapons such as the Original or the Sydney Sleeper or something.
Just some food for thought.