I only have done Jewel crafting so if the point is mute someone let me know.
What I am thinking is that, each craft should have at least 1 item it can craft in each tier that the other crafts can not craft, but is needed to craft a recipe in other respective crafts ..but are not gonna break any certain craft by making it so that they can not level up if they do not have the item that is needed to make the special recipes. These items would be for really nice skin’s of stuff that was already available or a stat bonus that would make the item wanted.
For instance a sword that has a jewel(this would be a special gem, not the current stock of them, maybe made by combining all gems in that tier)in the hilt, the weapon smith would need that jewel to make a certain sword. Each craft would each have an item that they could craft for each other craft so some sort of commerce could be built off of the need to buy items from other crafts.
It may be only that I have yet to do crafting on another alt, and this may be in there but from what I have seen I don’t see it.
And if that’s too much to ask for how about each craft can make an item per tier that is used exclusively for the Mystic Forge ….so its not needed to make any said item from a craft but will combine with other crafts special items to craft stuff at the forge.
I think either of these idea’s will boost the economy and provide a means for some commerce that is needed.