Hello! New to the forums here but I had an idea(s) that I wanted to share with you all for potential feedback or implementation regarding Minor faction Diplomacy, AI targeting, and ship subtypes.
Firstly as a preface, I have not yet played Sins II, but I have been keeping track of its development, so some things I mention might already be implemented, or at odds, with current design so apologies in advance!
Currently, in Sins I with the DLC you're currently able to take an envoy Cruiser and take over a Minor faction, essentially giving it vassal status, but being forced to keep your envoy inside at all times using goodwill missions. It's somewhat immersion breaking to accidently move it and suddenly the entire gravity well becomes hostile suddenly, and having no control over the development/ships/facilities feels kind of weird, like you're essentially mind controlling them with a binary ability, and as soon as you so much as move that envoy they would target it like any other military ship. None of this is a problem, as much as a weird "gamey" mechanic.
My suggestions are a bit two fold, I'd like the establishment of a Civilian/Military distinction between different vessels with the intent to change how AI prioritizes targets. Enemy "Player" NPCs would not be affected, Pirates would prioritize Civilian vessels unless of significant military presence, and Minor Factions would not target Civilian Vessels at all unless if your current relationship is Hostile or worse. Civilian vessels would pretty much be any ship with no/minimal weapons. As a player, you would be able to set this as a doctrinal change either fleet/planet/empire wide. This is to not only differentiate strategies but also make the enemy forces feel more alive.
The second half of this would be to remove the diplomatic immunity ability from envoys (as a pirate or enemy listening to that made little sense regardless) but would also allow them to reach NPC planets without getting harassed. A safety timer could be implemented for Military vessels entering the well, allowing for escorts but no occupation forces.
Once an Envoy has made contact to a neutral planet, the Envoy becomes a dockable ship (like the current Squadrons), and the planet becomes interactive. From here, the entire system changes drastically.
Options appear for things like Planetary Development, Research development, Military development, Industry, etc. But these are resource sinks and mission rewards rather than one time use and could actively augment the Minor faction in the described ways. However, alongside these constructive options would be exploitative ones, sowing discontent, extracting resources, or even controlling facilities. All of these options would be attached to a pie chart suggesting support for your empire amongst the population (with potential for randomized beliefs etc.), If your empire has a certain threshold of support, a timer bar like the pirate raids starts rising towards assimilation of the Minor faction.
Beneficial investment can actively improve the planet before assimilation, and is the most consistent way to gain support but it would still be relatively slow. Conversely, exploiting the populace might lead to lower support but if you're the biggest dog in town, who cares right? These progress bars would be individualized towards each player, and would not disappear even if support was lost (to prevent someone outbidding you at the last moment essentially), although it would likely decay over time without some attention. This could lead to an interesting sunken cost fallacy between multiple empires fighting for political control of the Minor faction, all players are contributing to the eventual strength of the planet, and the Minor faction would be more than happy to reap the rewards of it's neutrality.
Significant maluses or bonuses can come into play as well such as previous minor empire destruction/assimilation, trade with the faction, culture spread, pirates destroyed, civilian targets engaged etc. Making sure not to punish the player too hard for choices they HAD to make, like destroying an enemy military.
From an asymmetrical perspective, races can and should have different approaches to all interactions with said planet, although I'm not going to suggest all the ways.
I hope you find some use out of this, perhaps some of this can help in the long term, but either way I'm happy to watch the game grow and I'm sure it'll be fantastic when it's completed!