Actually, that's worth considering. Micro-drones are inherently disposable anyway. If you're using a 3-4 mm drone, you don't care that the opposition knows it was a drone; they're tiny, not invisible, and not a secret. If a dozen drones all tried for the mouth (or the drone is a skin-penetrating dart), one is sure to get through. Until we all have counter-drone tech.
If the drone is going to get up close and personal with the target, there are any number of toxins and venoms that would be more practical than nerve gas.
And I expect the researchers will consider each and every one. Which deadly weapon they settle on is less important than that micro-drones can be weaponized.
