Would you be able to add drones to the aliens with your mod or make a separate mod if you're interested enough?
One could only add a drone to an existing alien race by having it replace one of the existing ranks, e.g. I could replace some cyberdiscs by drones. Terrorist units are a good candidate for this, as most races have two ranks using the same unit, but it would mean there'd be lower numbers of the original units in missions.
And yes, it would be better to do this as a separate mod. No sense in forcing a player to accept a change in alien races to be able to use some new early-game human tech.
Maybe a flying drone that spots for the aliens, such as those HL2 combine camera drones.
Okay, I'll admit I've been thinking about some early- to mid-game flying human units too. But I keep running into game balance issues. Easily replacable, psi-immune, unarmored flying scouting drones that can even be used indoors would give the player a significant advantage. Making such drones prohibitively expensive makes no logical sense. So I don't want to make the game this much easier by creating such units.
The grenade launcher drone looks like something you could have all the way through. What's its ammo capacity? Would you be able to give it ammo to reload itself? I would say, so long as an operative is next to the drone both of them will use up TUs when you reload ammo for the drone within the inv. Might not be viable to have an op as a mule haha carrying huge rockets unless you have the smaller rockets mod. Just an idea.
The GL variant has power 40, even less than a grenade, making it unsuitable for late game. Its accuracy is absolutely horrible, but what would you expect from a turn-of-the-millenium remote-controlled mini-drone? And the ammo capacity is 15, meaning it is quite easy to run it dry.
Sure, increasing the ammo capacity is just a matter of rewriting one number, but a huge ammo capacity makes little sense both logic-wise and balance-wise. Realoading it by having a soldier reload it is currently beyond the limits of modding, indeed beyond the limits of the code.
As for a mule drone, the problem is that the inventory is the same for all units, which means you have to either make the inventory unavailable (like with UGVs) or accept the fact that the mule could use any item you give it (so you could have the mule use medkits or fire weapons).