Something like in aoe2 when a farm is depleted have it play a simple non intrusive sound when a villager/settler becomes/is idle.
Two ways it can work
What do you think?
If its an optional sound sure.
I think the idea is sound, specifically play a sound the moment the villager goes idle, and then also a once off sound to remind you. I think a slight addition to this idea would be a flashing icon, but very subtle as there aren’t any flashing mini-map icons.
Then you would know that a villager is idle, you know where and it keep popping up without being to irritating.
But I like the idea about the sound.
There’s already a pop up on the screen when a vill is idle. The sound will start to become horrible in mid-late game if they add that. 
Imagine the AOE2 farm depletion sound…
If there are people who need it, maybe someone can do a mod.
this would drive me insane xD im already getting OCDs from the little pop up in the corner
It would be interesting to add customizable notifications like this. I think 1 idle villager might be too much, but 5 going idle (or whatever level you set it to) could be useful. Potentially also a notification when you train a unit and you only have so much pop space left (threshold of maybe 3 or 4?) so that you can get a house up in time.
Or really anything that Twitch chat might tell a streamer to check. Think !house or !vill.
Not sure if this can be tackled with mods, but it would be cool.
I think the sound might be annoying potentially unless it’s a subtle sound
The farm exhaust sound is probably the most annoying sound i ever heard.
Followed by the house block, and monks conversations.