For new players it would be potentially helpful to know when a new stockpile is needed and for players with big towns they may wish to have to options to get notifications of where stockpiles fill up so they can either use that .aerial up or create a new area.
How i see it going:
name stockpiles or descriptions: weaver/mason stockpile or food/stone stockpile or upper level/outside stockpile
When: when a stockpile is full or almost full
Action: player gets a notification on i button saying “Mason stockpile full”
Reason: to stop stockpiles being full and material littering the town
This would be a good feature, as long as it was toggle-able as you mentioned. Especially later on when we will have big cities, and potentially dozens of stockpiles. Those notifications would start to get annoying fast.
Also if you were to ask me I would say it is arguable how necessary for it to tell you that your stockpile is full, because a quick glance will tell you all you need to know. I dunno it seems like a lot of pop-ups for not so important things.
If you have say a food pile the is empty but is in a mine you may not check it before villagers have to walk a fair way away from the mine location to eat and as u say it would need to be Toggleable