Self descriptive. Nations can capture trade outposts on cities the same way that they can capture space stations. These trade outposts collect a fixed % of every sale as a tax. This promotes ground and “combined arms” battles (over the control of the post) involving foot combat and ships for a much more dynamic combat environment, while also adding another purpose to nations. This further incentivizes player counter-piracy so that people are more likely to use outposts controlled by your nation.
Think of this as a “seal of safety” IE (nation A) has a reputation of protecting their outposts. This could lead the player to choose a trade post operated by A more frequently than a post controlled by (nation B) who is known for harassing traders, even if the profits to trading at a B outpost are more lucrative!
In essence, the idea is a way of making trade runs even more dynamic and requiring some wit and know how to really succeed.
Stop me if this is too much work, but this could even be expanded upon to add trade missions to the current space stations, adding some real value to controlling a station and encouraging minor nations to flex their potential for control.