Since the crafting recipes are done with slots, I'd really like to see a slot which is purely aesthetic on some items to allow for increased variation. Alternatively, the ability to put a material in the additive element slot which doesn't enhance the items abilities.
For example, a sword could have a slot for the pommel or in the hilt that allowed people to put a gemstone in there or even a metal that could also be used in forging the blade, but using it in this instance does not increase the quality of the item, just the aesthetic value.
This would allow people to leave the slot empty if they were purely trying to create a functional item, but a greater degree of customisation to add something to crafting. There would be a cost in terms of using materials without any tangible gain, but would be worth it to alolow a greater degree of creativity.