This would probably be difficult, but it would be cool if you made one of those DARPA mule robots.

a siren function for the "limb of the law" drone

A biped drone

fun idea: try doing the hunter-killers from the terminator movies. that would be awsome if you can do that.

What about a terminator or human sized robot drone that is armed with variable weapons that is able to traverse inside enemy buildings.

yes

Maybe a transformer or cameleon (of course cameleon can be invisible)

A walking, shooting star wars all terrain armored assault vehicle, the At-At walker

I'm not sure about that but the idea of hacking drones just by a simple command seems a bit easy. I though about a hacking difficulty level where the user must do some tricks like finding a code before a timer breaks the hacking console.
Bigger would be the drone (Health+firepower as factor), harder would be the hacking.

Oh and by the way, a melee mecha drone (not like the spider one) that crushes enemies with its bare fists would be epic, maybe. :3

we wanted to make flying melee drone with swords, would that be epic?

Yes

I had the idea of plane drones. That means drones that can't hover in air, but have special weapons instead like dropable bombsor lasers. It doesn't sound very original considering we already have planes in Gmod, but it would justify the size of the mothership's platform that could serve to launch planes. ^^

Oh and about bomb drones, why wouldn't we have a RC kamikaze car ?

massive air drone with many guns)

Guess that Rico Bond wants gunships ? Maybe dropship drones with more soldier capacity and few guns.

Mybe you could add enemy AI that would be cool