Having heard that you wanted some structures to increase pop-cap, I wondered if this could be combined with an idea I had for civilian space structures.
The background: having seen how Ascendancy seeks to show the IR liberalising, and the NR's traits as a democracy, I wondered if this could be shown by civilian structures.
The NR gets civilian structures that provide economic benefits (details below). These have a lower price than military structures. If Upkeep was added to structures, these would go without. They would have very low health though, and could be easily destroyed by weak units. Any economic benefits would have a maximum limit per system so you don't build loads to get incredible cheap units and fast build times.
The IR, EotH, and the Warlords also have civilian structures (same types and effects as the NR, mind). These are much more expensive than NR ones, and provide lower numerical values for benefits. Their military structures would nonetheless be cheaper (i.e.: a greater focus on the military in a military dictatorship). The EotH would have the cheapest civ structures and most expensive military ones out of the group, followed in order by the IR, Zinj faction and then the other warlords.
To show Pelleaon liberalising things post- Daala, the IR's structures would get much cheaper in his GCs in era 5, with military structures going up in cost alittle. This would help in era 5 when they have few planets but need higher pop-cap (relating to your comment on the playthrough about how factions with less territory might need higher pop-cap).
The structures could be:
Colony- higher pop cap raises.
Storage depot/warehouse- faster build times/ lower upkeep costs (perhaps 2 structure types here for either effect).
Hyperspace E-Booster- Faster trade route travel times.
(possible thoughts:
They could have an effect across multiple systems (since they would take up existing space structure slots and should be kept to a minimum). For example, structures in Caridan space can mildly affect neighboring systems.
Also: Like in the original Command and Conquer- the NR would not be able to shoot civilian structures (same for EotH all eras, and IR era 5), but they would not count in victory conditions.)
Is any of that useful?