I had been thinking a while ago how cool it would be if we could take over starbases with troop transports. I don't know if something like this could be done with modding (cause I'm not a modder), but it seems that it would be a patch/expansion intricate concept moreso.
Anyway, the thought goes like this:
Starbase Garrison tech in the soldiering tech tree, as an offshoot like the Planetary Defense techs.
Tech 1 Starbase Garrison , allows Security Office Starbase Module: gives 100 troops to starbase, only one per starbase allowed.
Tech 2 Zero-G Infantry , allows Infantry Barracks Module: +5 solidering on starbase with this module; increases starbase troop allotment +500, troops must be supplied by troop transport (more on this later), up to 4 allowed per starbase, must have Security Office installed first. Also allows Starbase Invasion.
Tech 3 offshoot Starbase Recruitment, allows Recruiting Office module: +10 morale to planets within starbase radius. This module generates troops to fill starbase allotment on its own without having to carry troops to it via transport (number of troops generated depends on numerous factors like influence and happiness of population and proximity to happy planets of owner or unhappy planets of opposition). (Potentially may allow starbase to 'assign' another starbase to where it's troops go when that base is over allotment, like Asteroid bases assign resources, but that may be too much coding, I don't know.)
Tech 3 Advanced Zero-G Training, allows Zero-G Holographic Training Simulator Module: +15 soldiering on starbase with this module; only one allowed per starbase, must have at least one Infantry Barracks installed first. Module costs extra 500bc to construct.
Tech 4 Marine Barracks (req also Space Marines Tech), allows Marine Barracks Module: +10 soldiering on starbase with this module; increases starbase troop allotment +500, troops must be supplied by troop transport, up to 2 allowed per starbase, must have at least one Infantry Barracks installed first. This module also enhances the Recruiting Office module by bumping the morale boost to nearby planets +5 and increasing the rate of recruitment for the starbase (double the rate depending on the math used to determine recruitment).
Tech 5 Special Ops, allows Spec Ops Barracks module and Spec Ops Training Facility module. Spec Ops Barracks Module: +10 soldiering on starbase with this module; increases allotment +500; only allowed one per starbase, must have at least one Marine Barracks installed. Spec Ops Training Facility module: +10 soldiering on starbase with this module, additional +15 if starbase has Spec Ops Barracks; must have Advanced Zero-G Training module installed; costs additional 200bc to install; only one allowed per starbase.
Starbase modules could be added to any type of starbase unless otherwise noted. Troop transports and colony ships would get an option when entering the same space as a starbase, much in the same way constructors do already, that would allow them to 'Dock' with starbase. Then when moving them away from square, they would get the same slider bar option as they do when leaving a planet, allowing you to leave troops there or pick them up. Note that module bonuses only apply to the starbase and do not follow the troops themselves. And, like when people are in transport aboard ships, these troops do not bring in tax revenue (or maybe reduced revenue) while stationed aboard a starbase.
These are a lot of increases for the Starbase Soldiering, but very limited in troop allotment compared to what you could bring against them in multiple troop transports.
By the same token, opposing race troop transports would get the option to invade the starbase like a planet. First the defenses would have to be taken out, which means another script for the attacking fleet to blow up the base or take tactical action against the defenses and not the superstructure itself. This should reduce the effectiveness of the weapons in that fleet against the starbase, and those weapon modules would have to be removed from the starbase in any event of a fleet Victory against the starbase (I know a lot of coding changes and stuff). It would be like a planetary invasion where all the ships in orbit have to be gone first, then the transport could get the invade option. Unlike planetary invasion though, one doesn't get the options of Tidal Disruption, Mini-Soldiers (they would blow holes in things they weren't supposed to), Mass Drivers, Propoganda, etc.
The major point of note would be that at some point it would simply be easier to blow the stuff up than to take it over, so the Race AI would have to be tweaked a bit to make sure they were interested in invading starbases instead of just annihilating them (dependant upon the race in question of coarse, like the Drengin might want to take them over, while the Korath would be more interested in just erasing them from the galaxy).
Anyway, just a few thoughts I wanted to put out there. Maybe too late for the expansion, but possibly a patch for expansion buyers...?
(Edit - BTW, this is the second incarnation of my idea. The first might have other aspects to it that I forgot, but is on a compy whose vid card just fried so is inaccessible for a little bit)