I tried adding a drone to my games once. I did not like how with hidden nationality the AI attacks you even if you are their ally. Does not compute and its a little silly. If the purpose is to play a conquest game, then I guess it works.
I propose a new level of stealth for drone planes. I've tested in my games planes with different levels of stealth:
-Gen 1 =(ww2) is standard.
-Gen 2 =(cold war) is standard but now faster due to jet turbines.
*Stealth levels begin*
-Gen 3 =stealth ability active in planes.
-Gen 4 =stealth + invisible active in planes. (Drones fit here)
I gave my drones invisibility to simulate stealthiness, but not 'stealth' to simulate a lesser stealth than real 'stealth' planes. No hidden nationality as a personal preference as it looks sillier to attack an ally, than to silently attack an enemy with invisibility.
Also I gave the more advanced AA, and gen 4 jets the 'can detect invisible' ability.
Now here comes the interesting part:
The AI will not build them as they will be inferior units to the 4th generation jets, BUT I think I have a system depending on what you wanna do.
-If drones are acquired through auto-production only, then they can work as I mentioned. Fair for both AI and humans.
-If drones are acquired through the build-que only, then they will still function as I proposed, but the AI will not build. Unfair to the AI.
-If drones are acquired as an extra strike due to 'intelligence' (enslaving from lethal bombard), then it works a little different:
A: You could set the drone as 'cruise missile' for it to have a single strike, and it will no longer be able to be intercepted, which will also render the 4th generation invisibility ability useless.
B: You could alternatively leave them as the original idea I described (weak invis flying unit), but the drone count might go nuts due to enslaving. Also unfair to the AI, since the AI will not bombard you if you have a decent anti air defense.
Personally what I would do since I dont mind just for the sake of the AI is to make drones auto-produce, and able to capture as well. Give them strong lethal bombard, so maybe the AI can keep up as well, but that's just me.
As far as mercenaries go I barely have a clue. In my mod this is how I get mercenaries:
-Only police officers are draft-able
-If I ever draft so that I can use my military while leaving behind someone to take care of my cities, after the conflict is over the left over police officers I would dump and upgrade to mercenaries with the ability to enslave oil, which can upgrade to mediocre tanks.
I basically use them as a way to steal resources to build up your tanks if you lack the right resources, or as a way of having a different type of tank if you do have the resources, but these tanks are a little different from the normal tanks just for fun sakes. Yes the military contractors have hidden nationality.