To add some clarity to the conversation, as it functions in game so far, Steele can only have one drone-type aid in combat at a time. The combat is coded in such a way that does not allow multiple drones/companions to attack in a row. It is possible for friendlies and hostiles to also have there own drones, but again each will only have one that attacks. If multiple drones are a thing (not counting unique combat encounters as those are set up differently), the combat portion of the drone code will need to be revamped.
As for perks and advantages, tech specialists can have a perk for an automatic Attack Drone, this will enable Steele to always have a drone in combat as long as Steele's shields keep it active. However, equipping any drone or companion in the accessory slot, will replace that perk with a standalone drone. Whether or not that drone requires shields is dependent on if the drone item is an actual robot and if it is self-powered. Another advantage engineers have is when picking up a Tam-wolf during the Stellar Tether mission, the drone will be completely fixed, whereas other classes will get a damaged version. The advantage to which become more obvious as Kara's second quest allows the drone to be fixed or upgraded.
As it was noted in its original document, the varmint is supposed to function in combat like a drone, so I had made it as such. This means that yes, it also replaces the Attack Drone perk when the leash is equipped. Again, the limitation is that the combat code only handles one combat drone attack per turn, so it doesn't really account for both perk and accessory drones.
The siegwulfe is still a work-in-progress item, so it may be tweaked later down the line when more testing and input is given about it. So far, the bimbo variant may be the most over-powered variant against opponents that are not immune to lust. The original document mentioned that it could be a tech-spec-only item, though it did not really end up that way. Perhaps engineers and/or the Attack Drone perk will have an added bonus to it? That has yet to be discussed however.
As for my opinion on a secondary slot reserved just for drones/companions, I would say that it would only be a viable option if drone combat was a really big deal in the game--like if Steele had a huge cache of possible drones to obtain and NPCs use it regularly in combat. Otherwise, keeping them as just accessory slot items is fine with me as it encourages the player to do some item management if they really want to use one, allowing all drones to have a more novel aspect.