I know it is late in development, so this would probably have to wait for after v1. 

A big annoyance in unit design is the way upgrades work now. Specifically, when iron-costing and crystal-costing items are all available for upgrade.

Is there a way to make magic swords and mundane swords, metal armor and magic armor, etc, into separate categories? While it is possible you would sometimes want the "best item period" on some unit designs, I think players would usually want control over resource cost foremost. 

As it is now, once all research is completed, I find myself making new designs just to get back to units that only used metal.

If separating makes me create 2 new designs to adapt, it'll save me from making 5+ other designs to avoid adding crystal cost to proven designs.