It would be neat if I could designate an amount of a resource as reserve. For example potters and smelters would be able to use coal, but won't deplete it completely, leaving me in the dark or unable to burn a glade event.
You can do this already. Open the main warehouse and you can set a reserve number. This prevents your crafters from using the resource once it reaches that number; it will not prevent your citizens from using consumables (use consumable control for that) or from being burned in the hearth (use hearth controls for that).