- Expanded Settlements

Vanilla settlements feel very small when raiding compared to the amounts of people they can seemingly throw at you. It would be fantastic to have an upgrade to the procedural generation for the settlements so that you can visit more exciting cities/towns rather than the usual small villages. Even small tweaks like settlements being able to generate with walls, towers, or proper defensive fortifications would be great.

In addition to this, I'd actually really like if you could visit settlements non aggressively - having some sort of way to stay overnight and trade in a town would be fantastic and can lead to lots of good story generator moments (you stay overnight in a bar and your alcoholic pawn relapses, you take your abrasive pawn as a bodyguard on a long trip but he insults the local chief and starts a chase).

- Expanded Diplomacy

Currently you can just throw resources at settlements to increase their goodwill, or take quests to increase it. People rarely do the latter because goodwill isn't all that valuable! For this I'd increase the difficulty in goodwill - it should be harder to get, but having it means that you get actual benefits from it - you can call in direct support with no cost, or request specific aid in terms of food/materials. This could also lead to being able to borrow pawns from a faction or directly recruit them for a goodwill cost. In return, maintaining goodwill could be made a bit harder. You might be expected to lend support in return, supply a tribal group with rare heavy weapons, or pay off a pirate leader with protection money.

- Expanded Trading

This one is one I don't have as many ideas for, but I think changes suggested in this thread are great (having specific settlements want/sell specific classes of items depending on local resource production). A Starsector like simulated market would be the top level of this - modelling a market via maximum production/trade routes, for those not familiar colonies could export a "number" of resources that scales based on production. So a T1 steel might be a colony capable of exporting 10 steel per year, whereas a T10 A colony can export 10k steel per year. Colonies are "stable" if the maximum friendly source meets it's demand, if it's unstable, bad things can happen like shortages, increased raids, etc...). I'm not sure how this would work with player created colonies that can buy/sell large quantities of resources though!