"Tho speaking of which, is it possible for you make a feature of vassal a faction (yours/other faction's) in the some future update?"
@Histidine
I would like to second this. Maybe as part of the diplomatic expansion?
This is just one man's opinion, but it would be nice to implement some kind of war score system. The Sector has a lot more static history compared to the sudden and sweeping changes frequently observed during Nexerelin playthroughs.
In real life, most of the time, the border changes are rarely the same as the frontlines at the end of the war. There is often a peace negotiation, where the territories changing hands are usually determined by the "staying power" of the warring sides at that point of the conflict.
So my suggestion is -and I know it is a lot of work- that if one side reaches exhaustion or for some other reason wants to sign a peace deal, AND the other side is exhausted enough to be willing to negotiate, then the status of the occupied markets should be decided based on the current negotiating position of the two parties.
For example, if the aggressor took a lot of planets but is exhausted and wants to negotiate, then the markets staying under his control should be quite low.
Additionally, if a power is more interested in projecting influence than outright conquest (Tri-Tachion for eg) it could aim for making the other side a vassal or force some kind of unequal relationship (maybe with different levels of dependence, based on the power relation?). Also, vassals should naturally strive to become independent over time, especially if the overlord weakens.
It would also give a nice option to the player to create one or more vassal states instead of the "autonomous colonies". Right now they feel like individual city-states and in my opinion, organizing them into one or more vassals would make a lot more sense (the idea being that they would be strong enough to better defend themselves, but not strong enough to challenge the player - hence the possibility to create more of them: divide and conquer).
Complementing this, markets conquered before a peace settlement should have a very strong "occupied-rebellion ongoing" trait, which shouldn't go away until peace settlement, because of the obvious guerilla activities coordinated by the original owner, and as a result, these planets should not contribute to the occupier's stats in any positive way until a peace deal. After the peace deal, regular unrest should continue, but it wouldn't be a controlled one by the original owner (maybe an option for clandestine support?) and should decline over time.
Anyway, just a bunch of ideas for a more realistic political system and a more realistic model for power dynamics. I know it's very hard to implement, but hey, you never know