Would CoO detect drone attacks? Some people argue it can only detect living beings.
Depends on the users CoO.
Normal CoO detects the location, feelings, and power of others.
Adv CoO, like Future Sight, is more about just scanning the overall environment.
So, I think base CoO allows you to detect living beings, and Adv CoO allows you to detect beyond living beings, while also potentially allowing you to see the future.
Considering Pre Time Skip Usopp's feat in Enies Lobby, sniping Spandam and Marines from the Tower of Justice, I'd say Post Time Skip Usopp can definitely deal with drones. Hide in Pop Green to tank bullet damage, then pop out to snipe drones.